Previously, we had warnings when a single page allocation took longer
than reasonably expected.  This was introduced in commit 63f53dea0c98
("mm: warn about allocations which stall for too long").

The warning was subsequently reverted in commit 400e22499dd9 ("mm: don't
warn about allocations which stall for too long") but for reasons
unrelated to the warning itself.

Page allocation stalls in excess of 10 seconds are always useful to debug
because they can result in severe userspace unresponsiveness.  Adding
this artifact can be used to correlate with userspace going out to lunch
and to understand the state of memory at the time.

There should be a reasonable expectation that this warning will never
trigger given it is very passive, it starts with a 10 second floor to
begin with.  If it does trigger, this reveals an issue that should be
fixed: a single page allocation should never loop for more than 10
seconds without oom killing to make memory available.

Unlike the original implementation, this implementation only reports
stalls that are at least a second longer than the longest stall reported
thus far.

Signed-off-by: David Rientjes <rientjes@google.com>
---
 mm/page_alloc.c | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4706,6 +4706,36 @@ check_retry_cpuset(int cpuset_mems_cookie, struct alloc_context *ac)
 	return false;
 }
 
+static unsigned long max_alloc_stall_warn_msecs = 10 * 1000L;
+
+static void check_alloc_stall_warn(gfp_t gfp_mask, nodemask_t *nodemask,
+				   unsigned int order, unsigned long alloc_start_time)
+{
+	static DEFINE_SPINLOCK(max_alloc_stall_lock);
+	unsigned long stall_msecs = jiffies_to_msecs(jiffies - alloc_start_time);
+	unsigned long flags;
+
+	if (likely(stall_msecs <= READ_ONCE(max_alloc_stall_warn_msecs)))
+		return;
+	if (gfp_mask & __GFP_NOWARN)
+		return;
+
+	spin_lock_irqsave(&max_alloc_stall_lock, flags);
+	if (stall_msecs > max_alloc_stall_warn_msecs) {
+		pr_warn("%s: page allocation stall for %lu secs: order:%d, mode:%#x(%pGg) nodemask=%*pbl",
+			current->comm, stall_msecs / MSEC_PER_SEC, order, gfp_mask, &gfp_mask,
+			nodemask_pr_args(nodemask));
+		cpuset_print_current_mems_allowed();
+		pr_cont("\n");
+		dump_stack();
+		warn_alloc_show_mem(gfp_mask, nodemask);
+
+		/* Only print future stalls that are more than a second longer */
+		WRITE_ONCE(max_alloc_stall_warn_msecs, stall_msecs + MSEC_PER_SEC);
+	}
+	spin_unlock_irqrestore(&max_alloc_stall_lock, flags);
+}
+
 static inline struct page *
 __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
 						struct alloc_context *ac)
@@ -4726,6 +4756,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
 	int reserve_flags;
 	bool compact_first = false;
 	bool can_retry_reserves = true;
+	unsigned long alloc_start_time = jiffies;
 
 	if (unlikely(nofail)) {
 		/*
@@ -4990,6 +5021,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
 	warn_alloc(gfp_mask, ac->nodemask,
 			"page allocation failure: order:%u", order);
 got_pg:
+	check_alloc_stall_warn(gfp_mask, ac->nodemask, order, alloc_start_time);
 	return page;
 }

On Sat, 21 Mar 2026 20:03:16 -0700 (PDT) David Rientjes <rientjes@google.com> wrote:

> Previously, we had warnings when a single page allocation took longer
> than reasonably expected.  This was introduced in commit 63f53dea0c98
> ("mm: warn about allocations which stall for too long").
> 
> The warning was subsequently reverted in commit 400e22499dd9 ("mm: don't
> warn about allocations which stall for too long") but for reasons
> unrelated to the warning itself.
> 
> Page allocation stalls in excess of 10 seconds are always useful to debug
> because they can result in severe userspace unresponsiveness.  Adding
> this artifact can be used to correlate with userspace going out to lunch
> and to understand the state of memory at the time.
> 
> There should be a reasonable expectation that this warning will never
> trigger given it is very passive, it starts with a 10 second floor to
> begin with.  If it does trigger, this reveals an issue that should be
> fixed: a single page allocation should never loop for more than 10
> seconds without oom killing to make memory available.
> 
> Unlike the original implementation, this implementation only reports
> stalls that are at least a second longer than the longest stall reported
> thus far.

AI review: https://sashiko.dev/#/patchset/30945cc3-9c4d-94bb-e7e7-dde71483800c@google.com

The warn_alloc_show_mem() inside spin_lock_irqsave() does sound
problematic.

On Sat 21-03-26 20:03:16, David Rientjes wrote:
> Previously, we had warnings when a single page allocation took longer
> than reasonably expected.  This was introduced in commit 63f53dea0c98
> ("mm: warn about allocations which stall for too long").
> 
> The warning was subsequently reverted in commit 400e22499dd9 ("mm: don't
> warn about allocations which stall for too long") but for reasons
> unrelated to the warning itself.
> 
> Page allocation stalls in excess of 10 seconds are always useful to debug
> because they can result in severe userspace unresponsiveness.  Adding
> this artifact can be used to correlate with userspace going out to lunch
> and to understand the state of memory at the time.
> 
> There should be a reasonable expectation that this warning will never
> trigger given it is very passive, it starts with a 10 second floor to
> begin with.  If it does trigger, this reveals an issue that should be
> fixed: a single page allocation should never loop for more than 10
> seconds without oom killing to make memory available.
> 
> Unlike the original implementation, this implementation only reports
> stalls that are at least a second longer than the longest stall reported
> thus far.

Am all for reintroducing the warning in some shape. The biggest problem
back then was printk being too eager to stomp all the work at a single
executing context. Not sure this is still the case. Let's add printk
maintainers.
Also it makes some sense to differentiate stalled callers and show_mem
which is more verbose. The former tells us who is affected and the
second will give us more context and we want to get some information
about all of them. The latter can be printed much less often as it will
describe situation for a batch of concurrent ones.

> Signed-off-by: David Rientjes <rientjes@google.com>
> ---
>  mm/page_alloc.c | 32 ++++++++++++++++++++++++++++++++
>  1 file changed, 32 insertions(+)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4706,6 +4706,36 @@ check_retry_cpuset(int cpuset_mems_cookie, struct alloc_context *ac)
>  	return false;
>  }
>  
> +static unsigned long max_alloc_stall_warn_msecs = 10 * 1000L;
> +
> +static void check_alloc_stall_warn(gfp_t gfp_mask, nodemask_t *nodemask,
> +				   unsigned int order, unsigned long alloc_start_time)
> +{
> +	static DEFINE_SPINLOCK(max_alloc_stall_lock);
> +	unsigned long stall_msecs = jiffies_to_msecs(jiffies - alloc_start_time);
> +	unsigned long flags;
> +
> +	if (likely(stall_msecs <= READ_ONCE(max_alloc_stall_warn_msecs)))
> +		return;
> +	if (gfp_mask & __GFP_NOWARN)
> +		return;
> +
> +	spin_lock_irqsave(&max_alloc_stall_lock, flags);
> +	if (stall_msecs > max_alloc_stall_warn_msecs) {
> +		pr_warn("%s: page allocation stall for %lu secs: order:%d, mode:%#x(%pGg) nodemask=%*pbl",
> +			current->comm, stall_msecs / MSEC_PER_SEC, order, gfp_mask, &gfp_mask,
> +			nodemask_pr_args(nodemask));
> +		cpuset_print_current_mems_allowed();
> +		pr_cont("\n");
> +		dump_stack();
> +		warn_alloc_show_mem(gfp_mask, nodemask);
> +
> +		/* Only print future stalls that are more than a second longer */
> +		WRITE_ONCE(max_alloc_stall_warn_msecs, stall_msecs + MSEC_PER_SEC);
> +	}
> +	spin_unlock_irqrestore(&max_alloc_stall_lock, flags);
> +}
> +
>  static inline struct page *
>  __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>  						struct alloc_context *ac)
> @@ -4726,6 +4756,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>  	int reserve_flags;
>  	bool compact_first = false;
>  	bool can_retry_reserves = true;
> +	unsigned long alloc_start_time = jiffies;
>  
>  	if (unlikely(nofail)) {
>  		/*
> @@ -4990,6 +5021,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>  	warn_alloc(gfp_mask, ac->nodemask,
>  			"page allocation failure: order:%u", order);
>  got_pg:
> +	check_alloc_stall_warn(gfp_mask, ac->nodemask, order, alloc_start_time);
>  	return page;
>  }
>  

-- 
Michal Hocko
SUSE Labs

On Mon, 23 Mar 2026, Michal Hocko wrote:

> On Sat 21-03-26 20:03:16, David Rientjes wrote:
> > Previously, we had warnings when a single page allocation took longer
> > than reasonably expected.  This was introduced in commit 63f53dea0c98
> > ("mm: warn about allocations which stall for too long").
> > 
> > The warning was subsequently reverted in commit 400e22499dd9 ("mm: don't
> > warn about allocations which stall for too long") but for reasons
> > unrelated to the warning itself.
> > 
> > Page allocation stalls in excess of 10 seconds are always useful to debug
> > because they can result in severe userspace unresponsiveness.  Adding
> > this artifact can be used to correlate with userspace going out to lunch
> > and to understand the state of memory at the time.
> > 
> > There should be a reasonable expectation that this warning will never
> > trigger given it is very passive, it starts with a 10 second floor to
> > begin with.  If it does trigger, this reveals an issue that should be
> > fixed: a single page allocation should never loop for more than 10
> > seconds without oom killing to make memory available.
> > 
> > Unlike the original implementation, this implementation only reports
> > stalls that are at least a second longer than the longest stall reported
> > thus far.
> 
> Am all for reintroducing the warning in some shape. The biggest problem
> back then was printk being too eager to stomp all the work at a single
> executing context. Not sure this is still the case. Let's add printk
> maintainers.

Thanks.

> Also it makes some sense to differentiate stalled callers and show_mem
> which is more verbose. The former tells us who is affected and the
> second will give us more context and we want to get some information
> about all of them. The latter can be printed much less often as it will
> describe situation for a batch of concurrent ones.
> 

Based on Vlastimil's suggestion I think this is trending in the direction 
of 10-second reporting windows system wide unless that doesn't work for 
some reason.  I do worry about reporting many stalls even without 
show_mem(), however.  In situations where the allocations are 
unconstained, all userspace goes out to lunch for 10 seconds and that can 
result in thousands of threads all reporting stalls and spamming the 
kernel log.

Idea is a 10 second threshold for reporting stalls and then only one stall 
report across a 10 second sliding window globally.

On Mon 2026-03-23 18:13:21, David Rientjes wrote:
> On Mon, 23 Mar 2026, Michal Hocko wrote:
> 
> > On Sat 21-03-26 20:03:16, David Rientjes wrote:
> > > Previously, we had warnings when a single page allocation took longer
> > > than reasonably expected.  This was introduced in commit 63f53dea0c98
> > > ("mm: warn about allocations which stall for too long").
> > > 
> > > The warning was subsequently reverted in commit 400e22499dd9 ("mm: don't
> > > warn about allocations which stall for too long") but for reasons
> > > unrelated to the warning itself.
> > > 
> > > Page allocation stalls in excess of 10 seconds are always useful to debug
> > > because they can result in severe userspace unresponsiveness.  Adding
> > > this artifact can be used to correlate with userspace going out to lunch
> > > and to understand the state of memory at the time.
> > > 
> > > There should be a reasonable expectation that this warning will never
> > > trigger given it is very passive, it starts with a 10 second floor to
> > > begin with.  If it does trigger, this reveals an issue that should be
> > > fixed: a single page allocation should never loop for more than 10
> > > seconds without oom killing to make memory available.
> > > 
> > > Unlike the original implementation, this implementation only reports
> > > stalls that are at least a second longer than the longest stall reported
> > > thus far.
> > 
> > Am all for reintroducing the warning in some shape. The biggest problem
> > back then was printk being too eager to stomp all the work at a single
> > executing context. Not sure this is still the case. Let's add printk
> > maintainers.

printk() is still a constraint. There is an API which allows to
offload printk() into a kthread but only few console drivers have been
converted so far. Most console drivers, including the most common
uart 8250, are still using the legacy loop in
printk()/console_unlock().

In addition, the new API introduced an emergency context which forces
synchronous flush of printk messages even for the converted console
drivers. The emergency context is currently used, for example, by
WARN() or RCU stall report. So, there always will be a risk that
too many pending messages might cause a stall.

> > Also it makes some sense to differentiate stalled callers and show_mem
> > which is more verbose. The former tells us who is affected and the
> > second will give us more context and we want to get some information
> > about all of them. The latter can be printed much less often as it will
> > describe situation for a batch of concurrent ones.
> >
>
> Based on Vlastimil's suggestion I think this is trending in the direction
> of 10-second reporting windows system wide unless that doesn't work for
> some reason.

This is a wise idea.

> I do worry about reporting many stalls even without
> show_mem(), however.  In situations where the allocations are
> unconstained, all userspace goes out to lunch for 10 seconds and that can
> result in thousands of threads all reporting stalls and spamming the
> kernel log.

Yeah, this looks scary even when all console drivers handled messages
in kthreads. I believe that printing details about all the stalled
tasks is not worth it. It might be enough to add an atomic counter
and print the number of stalled tasks within last 10 seconds.

> Idea is a 10 second threshold for reporting stalls and then only one stall 
> report across a 10 second sliding window globally.

I wonder if this even could be added to the existing watchdog,
aka report the number of stalled allocations in watchdog_timer_fn().

Best Regards,
Petr

On 3/22/26 4:03 AM, David Rientjes wrote:
> Previously, we had warnings when a single page allocation took longer
> than reasonably expected.  This was introduced in commit 63f53dea0c98
> ("mm: warn about allocations which stall for too long").
> 
> The warning was subsequently reverted in commit 400e22499dd9 ("mm: don't
> warn about allocations which stall for too long") but for reasons
> unrelated to the warning itself.
> 
> Page allocation stalls in excess of 10 seconds are always useful to debug
> because they can result in severe userspace unresponsiveness.  Adding
> this artifact can be used to correlate with userspace going out to lunch
> and to understand the state of memory at the time.
> 
> There should be a reasonable expectation that this warning will never
> trigger given it is very passive, it starts with a 10 second floor to
> begin with.  If it does trigger, this reveals an issue that should be
> fixed: a single page allocation should never loop for more than 10
> seconds without oom killing to make memory available.
> 
> Unlike the original implementation, this implementation only reports
> stalls that are at least a second longer than the longest stall reported
> thus far.
> 
> Signed-off-by: David Rientjes <rientjes@google.com>

I think, why not, if it's useful and we can reintroduce it without the
issues it had.
Maybe instead of requiring the stall time to increase by a second, we
could just limit the stall reports to once per 10 second. If there are
multiple ones in progress, one of them will win that report slot
randomly. This would also cover a stall that's so long it reports itself
multiple times (as in the original commit).

> ---
>  mm/page_alloc.c | 32 ++++++++++++++++++++++++++++++++
>  1 file changed, 32 insertions(+)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4706,6 +4706,36 @@ check_retry_cpuset(int cpuset_mems_cookie, struct alloc_context *ac)
>  	return false;
>  }
>  
> +static unsigned long max_alloc_stall_warn_msecs = 10 * 1000L;
> +
> +static void check_alloc_stall_warn(gfp_t gfp_mask, nodemask_t *nodemask,
> +				   unsigned int order, unsigned long alloc_start_time)
> +{
> +	static DEFINE_SPINLOCK(max_alloc_stall_lock);
> +	unsigned long stall_msecs = jiffies_to_msecs(jiffies - alloc_start_time);
> +	unsigned long flags;
> +
> +	if (likely(stall_msecs <= READ_ONCE(max_alloc_stall_warn_msecs)))
> +		return;

This check without lock is while I'm not worried about calling this
liberally (as you discuss in your self-reply).

> +	if (gfp_mask & __GFP_NOWARN)
> +		return;
> +
> +	spin_lock_irqsave(&max_alloc_stall_lock, flags);

This could make parallel stallers spin for no good reason while one that
has the lock is printing. I think we could use trylock here, and if it
fails, do nothing. Then it also shouldn't be necessary to disable irqs.

> +	if (stall_msecs > max_alloc_stall_warn_msecs) {
> +		pr_warn("%s: page allocation stall for %lu secs: order:%d, mode:%#x(%pGg) nodemask=%*pbl",
> +			current->comm, stall_msecs / MSEC_PER_SEC, order, gfp_mask, &gfp_mask,
> +			nodemask_pr_args(nodemask));
> +		cpuset_print_current_mems_allowed();
> +		pr_cont("\n");
> +		dump_stack();
> +		warn_alloc_show_mem(gfp_mask, nodemask);
> +
> +		/* Only print future stalls that are more than a second longer */
> +		WRITE_ONCE(max_alloc_stall_warn_msecs, stall_msecs + MSEC_PER_SEC);
> +	}
> +	spin_unlock_irqrestore(&max_alloc_stall_lock, flags);
> +}
> +
>  static inline struct page *
>  __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>  						struct alloc_context *ac)
> @@ -4726,6 +4756,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>  	int reserve_flags;
>  	bool compact_first = false;
>  	bool can_retry_reserves = true;
> +	unsigned long alloc_start_time = jiffies;
>  
>  	if (unlikely(nofail)) {
>  		/*
> @@ -4990,6 +5021,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>  	warn_alloc(gfp_mask, ac->nodemask,
>  			"page allocation failure: order:%u", order);
>  got_pg:
> +	check_alloc_stall_warn(gfp_mask, ac->nodemask, order, alloc_start_time);

But placed here it defeats the purpose to some extent, no? We'll only
learn about a stall that ended. With the shared 10s rate-limit, we
should be able to do it in the repeat loop for stalls in progress, as
the original commit did.

>  	return page;
>  }
>

On Mon, 23 Mar 2026, Vlastimil Babka (SUSE) wrote:

> On 3/22/26 4:03 AM, David Rientjes wrote:
> > Previously, we had warnings when a single page allocation took longer
> > than reasonably expected.  This was introduced in commit 63f53dea0c98
> > ("mm: warn about allocations which stall for too long").
> > 
> > The warning was subsequently reverted in commit 400e22499dd9 ("mm: don't
> > warn about allocations which stall for too long") but for reasons
> > unrelated to the warning itself.
> > 
> > Page allocation stalls in excess of 10 seconds are always useful to debug
> > because they can result in severe userspace unresponsiveness.  Adding
> > this artifact can be used to correlate with userspace going out to lunch
> > and to understand the state of memory at the time.
> > 
> > There should be a reasonable expectation that this warning will never
> > trigger given it is very passive, it starts with a 10 second floor to
> > begin with.  If it does trigger, this reveals an issue that should be
> > fixed: a single page allocation should never loop for more than 10
> > seconds without oom killing to make memory available.
> > 
> > Unlike the original implementation, this implementation only reports
> > stalls that are at least a second longer than the longest stall reported
> > thus far.
> > 
> > Signed-off-by: David Rientjes <rientjes@google.com>
> 
> I think, why not, if it's useful and we can reintroduce it without the
> issues it had.
> Maybe instead of requiring the stall time to increase by a second, we
> could just limit the stall reports to once per 10 second. If there are
> multiple ones in progress, one of them will win that report slot
> randomly. This would also cover a stall that's so long it reports itself
> multiple times (as in the original commit).
> 

I like that a lot, thanks.  Since part of the motivation is to correlate 
userspace unresponsiveness with page allocation stalls in the kernel, we 
increasingly lack that visiblity if a single long page allocation took 60 
seconds a month ago, for example, and we have to reach that threshold to 
report again.

The original patch ended up at line 4839 here:

4833)            }
4834)    }
4835) 
4836)    /* Caller is not willing to reclaim, we can't balance anything */
4837)    if (!can_direct_reclaim)
4838)            goto nopage;
4839) 							<===== HERE
4840)    /* Avoid recursion of direct reclaim */
4841)    if (current->flags & PF_MEMALLOC)
4842)            goto nopage;
4843) 
4844)    /* Try direct reclaim and then allocating */

Which looks like the right place to put it, but probably after the 
PF_MEMALLOC check.

If we set a minimum reporting threshold of 10 seconds and only report 
system wide every 10 seconds, I think this will work very well.  And, as 
you mention, this also reports stalls for allocations that never actually 
return.

I'll implement this and send out a formal patch for it.

On Sat, 21 Mar 2026, David Rientjes wrote:

> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4706,6 +4706,36 @@ check_retry_cpuset(int cpuset_mems_cookie, struct alloc_context *ac)
>  	return false;
>  }
>  
> +static unsigned long max_alloc_stall_warn_msecs = 10 * 1000L;
> +
> +static void check_alloc_stall_warn(gfp_t gfp_mask, nodemask_t *nodemask,
> +				   unsigned int order, unsigned long alloc_start_time)
> +{
> +	static DEFINE_SPINLOCK(max_alloc_stall_lock);
> +	unsigned long stall_msecs = jiffies_to_msecs(jiffies - alloc_start_time);
> +	unsigned long flags;
> +
> +	if (likely(stall_msecs <= READ_ONCE(max_alloc_stall_warn_msecs)))
> +		return;
> +	if (gfp_mask & __GFP_NOWARN)
> +		return;
> +
> +	spin_lock_irqsave(&max_alloc_stall_lock, flags);
> +	if (stall_msecs > max_alloc_stall_warn_msecs) {
> +		pr_warn("%s: page allocation stall for %lu secs: order:%d, mode:%#x(%pGg) nodemask=%*pbl",
> +			current->comm, stall_msecs / MSEC_PER_SEC, order, gfp_mask, &gfp_mask,
> +			nodemask_pr_args(nodemask));
> +		cpuset_print_current_mems_allowed();
> +		pr_cont("\n");
> +		dump_stack();
> +		warn_alloc_show_mem(gfp_mask, nodemask);
> +
> +		/* Only print future stalls that are more than a second longer */
> +		WRITE_ONCE(max_alloc_stall_warn_msecs, stall_msecs + MSEC_PER_SEC);
> +	}
> +	spin_unlock_irqrestore(&max_alloc_stall_lock, flags);
> +}
> +
>  static inline struct page *
>  __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>  						struct alloc_context *ac)
> @@ -4726,6 +4756,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>  	int reserve_flags;
>  	bool compact_first = false;
>  	bool can_retry_reserves = true;
> +	unsigned long alloc_start_time = jiffies;
>  
>  	if (unlikely(nofail)) {
>  		/*
> @@ -4990,6 +5021,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>  	warn_alloc(gfp_mask, ac->nodemask,
>  			"page allocation failure: order:%u", order);
>  got_pg:
> +	check_alloc_stall_warn(gfp_mask, ac->nodemask, order, alloc_start_time);
>  	return page;
>  }
>  
> 

Another option here if we're concerned about calling 
check_alloc_stall_warn() on every slowpath allocation is to check this 
right after calling into should_reclaim_retry().  We'd normally be looping 
in the page allocator if a single call is taking >10s.  That could output 
multiple stall warnings for a single page allocation, though, so in this 
case we'd probably want to (1) increase the amount of time between one 
warning and another beyond one second and (2) cap the output when some 
time duration is reached like 60 seconds.

Previously, we had warnings when a single page allocation took longer
than reasonably expected.  This was introduced in commit 63f53dea0c98
("mm: warn about allocations which stall for too long").

The warning was subsequently reverted in commit 400e22499dd9 ("mm: don't
warn about allocations which stall for too long") but for reasons
unrelated to the warning itself.

Page allocation stalls in excess of 10 seconds are always useful to debug
because they can result in severe userspace unresponsiveness.  Adding
this artifact can be used to correlate with userspace going out to lunch
and to understand the state of memory at the time.

There should be a reasonable expectation that this warning will never
trigger given it is very passive, it will only be emitted when a page
allocation takes longer than 10 seconds.  If it does trigger, this
reveals an issue that should be fixed: a single page allocation should
never loop for more than 10 seconds without oom killing to make memory
available.

Unlike the original implementation, this implementation only reports
stalls once for the system every 10 seconds.  Otherwise, many concurrent
reclaimers could spam the kernel log unnecessarily.  Stalls are only
reported when calling into direct reclaim.

Signed-off-by: David Rientjes <rientjes@google.com>
---
 mm/page_alloc.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -316,6 +316,14 @@ EXPORT_SYMBOL(nr_node_ids);
 EXPORT_SYMBOL(nr_online_nodes);
 #endif
 
+/*
+ * When page allocations stall for longer than a threshold,
+ * ALLOC_STALL_WARN_MSECS, leave a warning in the kernel log.  Only one warning
+ * will be printed during this duration for the entire system.
+ */
+#define ALLOC_STALL_WARN_MSECS (10 * 1000UL)
+static unsigned long alloc_stall_warn_jiffies;
+
 static bool page_contains_unaccepted(struct page *page, unsigned int order);
 static bool cond_accept_memory(struct zone *zone, unsigned int order,
 			       int alloc_flags);
@@ -4706,6 +4714,40 @@ check_retry_cpuset(int cpuset_mems_cookie, struct alloc_context *ac)
 	return false;
 }
 
+static void check_alloc_stall_warn(gfp_t gfp_mask, nodemask_t *nodemask,
+				unsigned int order, unsigned long alloc_start_time)
+{
+	static DEFINE_SPINLOCK(alloc_stall_lock);
+	unsigned long stall_msecs = jiffies_to_msecs(jiffies - alloc_start_time);
+
+	if (likely(stall_msecs < ALLOC_STALL_WARN_MSECS))
+		return;
+	if (time_before(jiffies, READ_ONCE(alloc_stall_warn_jiffies)))
+		return;
+	if (gfp_mask & __GFP_NOWARN)
+		return;
+
+	if (!spin_trylock(&alloc_stall_lock))
+		return;
+
+	if (time_after_eq(jiffies, alloc_stall_warn_jiffies)) {
+		WRITE_ONCE(alloc_stall_warn_jiffies,
+			   jiffies + msecs_to_jiffies(ALLOC_STALL_WARN_MSECS));
+		spin_unlock(&alloc_stall_lock);
+
+		pr_warn("%s: page allocation stall for %lu secs: order:%d, mode:%#x(%pGg) nodemask=%*pbl",
+			current->comm, stall_msecs / MSEC_PER_SEC, order, gfp_mask, &gfp_mask,
+			nodemask_pr_args(nodemask));
+		cpuset_print_current_mems_allowed();
+		pr_cont("\n");
+		dump_stack();
+		warn_alloc_show_mem(gfp_mask, nodemask);
+		return;
+	}
+
+	spin_unlock(&alloc_stall_lock);
+}
+
 static inline struct page *
 __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
 						struct alloc_context *ac)
@@ -4726,6 +4768,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
 	int reserve_flags;
 	bool compact_first = false;
 	bool can_retry_reserves = true;
+	unsigned long alloc_start_time = jiffies;
 
 	if (unlikely(nofail)) {
 		/*
@@ -4841,6 +4884,9 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
 	if (current->flags & PF_MEMALLOC)
 		goto nopage;
 
+	/* If allocation has taken excessively long, warn about it */
+	check_alloc_stall_warn(gfp_mask, ac->nodemask, order, alloc_start_time);
+
 	/* Try direct reclaim and then allocating */
 	if (!compact_first) {
 		page = __alloc_pages_direct_reclaim(gfp_mask, order, alloc_flags,

On 3/30/26 03:08, David Rientjes wrote:
> Previously, we had warnings when a single page allocation took longer
> than reasonably expected.  This was introduced in commit 63f53dea0c98
> ("mm: warn about allocations which stall for too long").
> 
> The warning was subsequently reverted in commit 400e22499dd9 ("mm: don't
> warn about allocations which stall for too long") but for reasons
> unrelated to the warning itself.
> 
> Page allocation stalls in excess of 10 seconds are always useful to debug
> because they can result in severe userspace unresponsiveness.  Adding
> this artifact can be used to correlate with userspace going out to lunch
> and to understand the state of memory at the time.
> 
> There should be a reasonable expectation that this warning will never
> trigger given it is very passive, it will only be emitted when a page
> allocation takes longer than 10 seconds.  If it does trigger, this
> reveals an issue that should be fixed: a single page allocation should
> never loop for more than 10 seconds without oom killing to make memory
> available.
> 
> Unlike the original implementation, this implementation only reports
> stalls once for the system every 10 seconds.  Otherwise, many concurrent
> reclaimers could spam the kernel log unnecessarily.  Stalls are only
> reported when calling into direct reclaim.
> 
> Signed-off-by: David Rientjes <rientjes@google.com>

Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>

Nit below:

> ---
>  mm/page_alloc.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 46 insertions(+)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -316,6 +316,14 @@ EXPORT_SYMBOL(nr_node_ids);
>  EXPORT_SYMBOL(nr_online_nodes);
>  #endif
>  
> +/*
> + * When page allocations stall for longer than a threshold,
> + * ALLOC_STALL_WARN_MSECS, leave a warning in the kernel log.  Only one warning
> + * will be printed during this duration for the entire system.
> + */
> +#define ALLOC_STALL_WARN_MSECS (10 * 1000UL)
> +static unsigned long alloc_stall_warn_jiffies;
> +
>  static bool page_contains_unaccepted(struct page *page, unsigned int order);
>  static bool cond_accept_memory(struct zone *zone, unsigned int order,
>  			       int alloc_flags);
> @@ -4706,6 +4714,40 @@ check_retry_cpuset(int cpuset_mems_cookie, struct alloc_context *ac)
>  	return false;
>  }
>  
> +static void check_alloc_stall_warn(gfp_t gfp_mask, nodemask_t *nodemask,
> +				unsigned int order, unsigned long alloc_start_time)
> +{
> +	static DEFINE_SPINLOCK(alloc_stall_lock);
> +	unsigned long stall_msecs = jiffies_to_msecs(jiffies - alloc_start_time);
> +
> +	if (likely(stall_msecs < ALLOC_STALL_WARN_MSECS))
> +		return;
> +	if (time_before(jiffies, READ_ONCE(alloc_stall_warn_jiffies)))
> +		return;
> +	if (gfp_mask & __GFP_NOWARN)
> +		return;
> +
> +	if (!spin_trylock(&alloc_stall_lock))
> +		return;
> +
> +	if (time_after_eq(jiffies, alloc_stall_warn_jiffies)) {

This could also be an unlock+return if the opposite (time_before()) is true,
reducing the indentation for the actual warning code.

> +		WRITE_ONCE(alloc_stall_warn_jiffies,
> +			   jiffies + msecs_to_jiffies(ALLOC_STALL_WARN_MSECS));
> +		spin_unlock(&alloc_stall_lock);
> +
> +		pr_warn("%s: page allocation stall for %lu secs: order:%d, mode:%#x(%pGg) nodemask=%*pbl",
> +			current->comm, stall_msecs / MSEC_PER_SEC, order, gfp_mask, &gfp_mask,
> +			nodemask_pr_args(nodemask));
> +		cpuset_print_current_mems_allowed();
> +		pr_cont("\n");
> +		dump_stack();
> +		warn_alloc_show_mem(gfp_mask, nodemask);
> +		return;
> +	}
> +
> +	spin_unlock(&alloc_stall_lock);
> +}
> +

On Sun 29-03-26 18:08:52, David Rientjes wrote:
> Previously, we had warnings when a single page allocation took longer
> than reasonably expected.  This was introduced in commit 63f53dea0c98
> ("mm: warn about allocations which stall for too long").
> 
> The warning was subsequently reverted in commit 400e22499dd9 ("mm: don't
> warn about allocations which stall for too long") but for reasons
> unrelated to the warning itself.

I think it makes sense to summarize reasons for the revert. I would
propose to change the above to somehting like
"
The warning was subsequently reverted in commit 400e22499dd9 ("mm: don't
warn about allocations which stall for too long") because it was
possible to generate memory pressure that would effectivelly stall
further progress through printk execution.
"
 
> @@ -4841,6 +4884,9 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>  	if (current->flags & PF_MEMALLOC)
>  		goto nopage;
>  
> +	/* If allocation has taken excessively long, warn about it */
> +	check_alloc_stall_warn(gfp_mask, ac->nodemask, order, alloc_start_time);
> +
>  	/* Try direct reclaim and then allocating */
>  	if (!compact_first) {
>  		page = __alloc_pages_direct_reclaim(gfp_mask, order, alloc_flags,

Is there any specific reason for this placement? Compaction can take
quite some time as well.

-- 
Michal Hocko
SUSE Labs

On 3/30/26 15:54, Michal Hocko wrote:
> On Sun 29-03-26 18:08:52, David Rientjes wrote:
>> Previously, we had warnings when a single page allocation took longer
>> than reasonably expected.  This was introduced in commit 63f53dea0c98
>> ("mm: warn about allocations which stall for too long").
>> 
>> The warning was subsequently reverted in commit 400e22499dd9 ("mm: don't
>> warn about allocations which stall for too long") but for reasons
>> unrelated to the warning itself.
> 
> I think it makes sense to summarize reasons for the revert. I would
> propose to change the above to somehting like
> "
> The warning was subsequently reverted in commit 400e22499dd9 ("mm: don't
> warn about allocations which stall for too long") because it was
> possible to generate memory pressure that would effectivelly stall
> further progress through printk execution.
> "
>  
>> @@ -4841,6 +4884,9 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>>  	if (current->flags & PF_MEMALLOC)
>>  		goto nopage;
>>  
>> +	/* If allocation has taken excessively long, warn about it */
>> +	check_alloc_stall_warn(gfp_mask, ac->nodemask, order, alloc_start_time);
>> +
>>  	/* Try direct reclaim and then allocating */
>>  	if (!compact_first) {
>>  		page = __alloc_pages_direct_reclaim(gfp_mask, order, alloc_flags,
> 
> Is there any specific reason for this placement? Compaction can take
> quite some time as well.

It seems fine to me - as longs as the slowpath is retrying for 10 seconds
and still can't obtain a page, there's a warning.

We don't catch cases when either the get_page_from_freelist() attempt,
direct compaction or direct reclaim attempt is what gets us over 10 seconds,
and at the same time it results in success. If that's a concern, we should
add another check_alloc_stall_warn() call under got_pg label (as the RFC
had) - I'm not sure it's all achievable with a single place with the call.

On Mon, 30 Mar 2026, Vlastimil Babka (SUSE) wrote:

> >> Previously, we had warnings when a single page allocation took longer
> >> than reasonably expected.  This was introduced in commit 63f53dea0c98
> >> ("mm: warn about allocations which stall for too long").
> >> 
> >> The warning was subsequently reverted in commit 400e22499dd9 ("mm: don't
> >> warn about allocations which stall for too long") but for reasons
> >> unrelated to the warning itself.
> > 
> > I think it makes sense to summarize reasons for the revert. I would
> > propose to change the above to somehting like
> > "
> > The warning was subsequently reverted in commit 400e22499dd9 ("mm: don't
> > warn about allocations which stall for too long") because it was
> > possible to generate memory pressure that would effectivelly stall
> > further progress through printk execution.
> > "
> >  

Will do!

> >> @@ -4841,6 +4884,9 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
> >>  	if (current->flags & PF_MEMALLOC)
> >>  		goto nopage;
> >>  
> >> +	/* If allocation has taken excessively long, warn about it */
> >> +	check_alloc_stall_warn(gfp_mask, ac->nodemask, order, alloc_start_time);
> >> +
> >>  	/* Try direct reclaim and then allocating */
> >>  	if (!compact_first) {
> >>  		page = __alloc_pages_direct_reclaim(gfp_mask, order, alloc_flags,
> > 
> > Is there any specific reason for this placement? Compaction can take
> > quite some time as well.
> 
> It seems fine to me - as longs as the slowpath is retrying for 10 seconds
> and still can't obtain a page, there's a warning.
> 
> We don't catch cases when either the get_page_from_freelist() attempt,
> direct compaction or direct reclaim attempt is what gets us over 10 seconds,
> and at the same time it results in success. If that's a concern, we should
> add another check_alloc_stall_warn() call under got_pg label (as the RFC
> had) - I'm not sure it's all achievable with a single place with the call.
> 

Right, the big idea here is that at least one of the allocations that is 
looping will run into the check_alloc_stall_warn().  We might miss a 
borderline case but the 10 seconds is already arbitrary and this is the 
placement where commit 63f53dea0c98 ("mm: warn about allocations which 
stall for too long") ended up before it was reverted.

On Sun, 29 Mar 2026 18:08:52 -0700 (PDT) David Rientjes <rientjes@google.com> wrote:

> Previously, we had warnings when a single page allocation took longer
> than reasonably expected.  This was introduced in commit 63f53dea0c98
> ("mm: warn about allocations which stall for too long").
> 
> The warning was subsequently reverted in commit 400e22499dd9 ("mm: don't
> warn about allocations which stall for too long") but for reasons
> unrelated to the warning itself.
> 
> Page allocation stalls in excess of 10 seconds are always useful to debug
> because they can result in severe userspace unresponsiveness.  Adding
> this artifact can be used to correlate with userspace going out to lunch
> and to understand the state of memory at the time.
> 
> There should be a reasonable expectation that this warning will never
> trigger given it is very passive, it will only be emitted when a page
> allocation takes longer than 10 seconds.  If it does trigger, this
> reveals an issue that should be fixed: a single page allocation should
> never loop for more than 10 seconds without oom killing to make memory
> available.
> 
> Unlike the original implementation, this implementation only reports
> stalls once for the system every 10 seconds.  Otherwise, many concurrent
> reclaimers could spam the kernel log unnecessarily.  Stalls are only
> reported when calling into direct reclaim.
> 
> ...
>
> +static void check_alloc_stall_warn(gfp_t gfp_mask, nodemask_t *nodemask,
> +				unsigned int order, unsigned long alloc_start_time)
> +{
> +	static DEFINE_SPINLOCK(alloc_stall_lock);
> +	unsigned long stall_msecs = jiffies_to_msecs(jiffies - alloc_start_time);
> +
> +	if (likely(stall_msecs < ALLOC_STALL_WARN_MSECS))
> +		return;
> +	if (time_before(jiffies, READ_ONCE(alloc_stall_warn_jiffies)))
> +		return;
> +	if (gfp_mask & __GFP_NOWARN)
> +		return;
> +
> +	if (!spin_trylock(&alloc_stall_lock))
> +		return;
> +
> +	if (time_after_eq(jiffies, alloc_stall_warn_jiffies)) {
> +		WRITE_ONCE(alloc_stall_warn_jiffies,
> +			   jiffies + msecs_to_jiffies(ALLOC_STALL_WARN_MSECS));
> +		spin_unlock(&alloc_stall_lock);
> +
> +		pr_warn("%s: page allocation stall for %lu secs: order:%d, mode:%#x(%pGg) nodemask=%*pbl",
> +			current->comm, stall_msecs / MSEC_PER_SEC, order, gfp_mask, &gfp_mask,
> +			nodemask_pr_args(nodemask));

Snould we use dump_page() in here?  It prints more info, does the
snapshotting thing.

> +		cpuset_print_current_mems_allowed();
> +		pr_cont("\n");
> +		dump_stack();
> +		warn_alloc_show_mem(gfp_mask, nodemask);
> +		return;
> +	}
> +
> +	spin_unlock(&alloc_stall_lock);
> +}
> +

On 3/30/26 05:17, Andrew Morton wrote:
> On Sun, 29 Mar 2026 18:08:52 -0700 (PDT) David Rientjes <rientjes@google.com> wrote:
> 
>> Previously, we had warnings when a single page allocation took longer
>> than reasonably expected.  This was introduced in commit 63f53dea0c98
>> ("mm: warn about allocations which stall for too long").
>> 
>> The warning was subsequently reverted in commit 400e22499dd9 ("mm: don't
>> warn about allocations which stall for too long") but for reasons
>> unrelated to the warning itself.
>> 
>> Page allocation stalls in excess of 10 seconds are always useful to debug
>> because they can result in severe userspace unresponsiveness.  Adding
>> this artifact can be used to correlate with userspace going out to lunch
>> and to understand the state of memory at the time.
>> 
>> There should be a reasonable expectation that this warning will never
>> trigger given it is very passive, it will only be emitted when a page
>> allocation takes longer than 10 seconds.  If it does trigger, this
>> reveals an issue that should be fixed: a single page allocation should
>> never loop for more than 10 seconds without oom killing to make memory
>> available.
>> 
>> Unlike the original implementation, this implementation only reports
>> stalls once for the system every 10 seconds.  Otherwise, many concurrent
>> reclaimers could spam the kernel log unnecessarily.  Stalls are only
>> reported when calling into direct reclaim.
>> 
>> ...
>>
>> +static void check_alloc_stall_warn(gfp_t gfp_mask, nodemask_t *nodemask,
>> +				unsigned int order, unsigned long alloc_start_time)
>> +{
>> +	static DEFINE_SPINLOCK(alloc_stall_lock);
>> +	unsigned long stall_msecs = jiffies_to_msecs(jiffies - alloc_start_time);
>> +
>> +	if (likely(stall_msecs < ALLOC_STALL_WARN_MSECS))
>> +		return;
>> +	if (time_before(jiffies, READ_ONCE(alloc_stall_warn_jiffies)))
>> +		return;
>> +	if (gfp_mask & __GFP_NOWARN)
>> +		return;
>> +
>> +	if (!spin_trylock(&alloc_stall_lock))
>> +		return;
>> +
>> +	if (time_after_eq(jiffies, alloc_stall_warn_jiffies)) {
>> +		WRITE_ONCE(alloc_stall_warn_jiffies,
>> +			   jiffies + msecs_to_jiffies(ALLOC_STALL_WARN_MSECS));
>> +		spin_unlock(&alloc_stall_lock);
>> +
>> +		pr_warn("%s: page allocation stall for %lu secs: order:%d, mode:%#x(%pGg) nodemask=%*pbl",
>> +			current->comm, stall_msecs / MSEC_PER_SEC, order, gfp_mask, &gfp_mask,
>> +			nodemask_pr_args(nodemask));
> 
> Snould we use dump_page() in here?  It prints more info, does the
> snapshotting thing.

But we have no page to dump, or did you mean something else? Maybe some part
of warn_alloc() (without its own ratelimit etc) could be extracted end reused.

>> +		cpuset_print_current_mems_allowed();
>> +		pr_cont("\n");
>> +		dump_stack();
>> +		warn_alloc_show_mem(gfp_mask, nodemask);
>> +		return;
>> +	}
>> +
>> +	spin_unlock(&alloc_stall_lock);
>> +}
>> +
>

Previously, we had warnings when a single page allocation took longer
than reasonably expected.  This was introduced in commit 63f53dea0c98
("mm: warn about allocations which stall for too long").

The warning was subsequently reverted in commit 400e22499dd9 ("mm: don't
warn about allocations which stall for too long") because it was possible
to generate memory pressure that would effectively stall further progress
through printk execution.

Page allocation stalls in excess of 10 seconds are always useful to debug
because they can result in severe userspace unresponsiveness.  Adding
this artifact can be used to correlate with userspace going out to lunch
and to understand the state of memory at the time.

There should be a reasonable expectation that this warning will never
trigger given it is very passive, it will only be emitted when a page
allocation takes longer than 10 seconds.  If it does trigger, this
reveals an issue that should be fixed: a single page allocation should
never loop for more than 10 seconds without oom killing to make memory
available.

Unlike the original implementation, this implementation only reports
stalls once for the system every 10 seconds.  Otherwise, many concurrent
reclaimers could spam the kernel log unnecessarily.  Stalls are only
reported when calling into direct reclaim.

Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Signed-off-by: David Rientjes <rientjes@google.com>
---
 v2:
  - commit message update per Michal
  - check_alloc_stall_warn() cleanup per Vlastimil

 mm/page_alloc.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -316,6 +316,14 @@ EXPORT_SYMBOL(nr_node_ids);
 EXPORT_SYMBOL(nr_online_nodes);
 #endif
 
+/*
+ * When page allocations stall for longer than a threshold,
+ * ALLOC_STALL_WARN_MSECS, leave a warning in the kernel log.  Only one warning
+ * will be printed during this duration for the entire system.
+ */
+#define ALLOC_STALL_WARN_MSECS (10 * 1000UL)
+static unsigned long alloc_stall_warn_jiffies;
+
 static bool page_contains_unaccepted(struct page *page, unsigned int order);
 static bool cond_accept_memory(struct zone *zone, unsigned int order,
 			       int alloc_flags);
@@ -4706,6 +4714,40 @@ check_retry_cpuset(int cpuset_mems_cookie, struct alloc_context *ac)
 	return false;
 }
 
+static void check_alloc_stall_warn(gfp_t gfp_mask, nodemask_t *nodemask,
+				unsigned int order, unsigned long alloc_start_time)
+{
+	static DEFINE_SPINLOCK(alloc_stall_lock);
+	unsigned long stall_msecs = jiffies_to_msecs(jiffies - alloc_start_time);
+
+	if (likely(stall_msecs < ALLOC_STALL_WARN_MSECS))
+		return;
+	if (time_before(jiffies, READ_ONCE(alloc_stall_warn_jiffies)))
+		return;
+	if (gfp_mask & __GFP_NOWARN)
+		return;
+
+	if (!spin_trylock(&alloc_stall_lock))
+		return;
+
+	/* Check again, this time under the lock */
+	if (time_before(jiffies, alloc_stall_warn_jiffies)) {
+		spin_unlock(&alloc_stall_lock);
+		return;
+	}
+
+	WRITE_ONCE(alloc_stall_warn_jiffies, jiffies + msecs_to_jiffies(ALLOC_STALL_WARN_MSECS));
+	spin_unlock(&alloc_stall_lock);
+
+	pr_warn("%s: page allocation stall for %lu secs: order:%d, mode:%#x(%pGg) nodemask=%*pbl",
+		current->comm, stall_msecs / MSEC_PER_SEC, order, gfp_mask, &gfp_mask,
+		nodemask_pr_args(nodemask));
+	cpuset_print_current_mems_allowed();
+	pr_cont("\n");
+	dump_stack();
+	warn_alloc_show_mem(gfp_mask, nodemask);
+}
+
 static inline struct page *
 __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
 						struct alloc_context *ac)
@@ -4726,6 +4768,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
 	int reserve_flags;
 	bool compact_first = false;
 	bool can_retry_reserves = true;
+	unsigned long alloc_start_time = jiffies;
 
 	if (unlikely(nofail)) {
 		/*
@@ -4841,6 +4884,9 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
 	if (current->flags & PF_MEMALLOC)
 		goto nopage;
 
+	/* If allocation has taken excessively long, warn about it */
+	check_alloc_stall_warn(gfp_mask, ac->nodemask, order, alloc_start_time);
+
 	/* Try direct reclaim and then allocating */
 	if (!compact_first) {
 		page = __alloc_pages_direct_reclaim(gfp_mask, order, alloc_flags,

Previously, we had warnings when a single page allocation took longer
than reasonably expected.  This was introduced in commit 63f53dea0c98
("mm: warn about allocations which stall for too long").

The warning was subsequently reverted in commit 400e22499dd9 ("mm: don't
warn about allocations which stall for too long") because it was possible
to generate memory pressure that would effectively stall further progress
through printk execution.

Page allocation stalls in excess of 10 seconds are always useful to debug
because they can result in severe userspace unresponsiveness.  Adding
this artifact can be used to correlate with userspace going out to lunch
and to understand the state of memory at the time.

There should be a reasonable expectation that this warning will never
trigger given it is very passive, it will only be emitted when a page
allocation takes longer than 10 seconds.  If it does trigger, this
reveals an issue that should be fixed: a single page allocation should
never loop for more than 10 seconds without oom killing to make memory
available.

Unlike the original implementation, this implementation only reports
stalls once for the system every 10 seconds.  Otherwise, many concurrent
reclaimers could spam the kernel log unnecessarily.  Stalls are only
reported when calling into direct reclaim.

Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Signed-off-by: David Rientjes <rientjes@google.com>
---
 v3:
  - initialize to INITIAL_JIFFIES per AI review so warnings are not
    suppressed in the first five minutes after boot
  - time_before(jiffies, a) -> time_is_after_jiffies(a)
 v2:
  - commit message update per Michal
  - check_alloc_stall_warn() cleanup per Vlastimil

 mm/page_alloc.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -316,6 +316,14 @@ EXPORT_SYMBOL(nr_node_ids);
 EXPORT_SYMBOL(nr_online_nodes);
 #endif
 
+/*
+ * When page allocations stall for longer than a threshold,
+ * ALLOC_STALL_WARN_MSECS, leave a warning in the kernel log.  Only one warning
+ * will be printed during this duration for the entire system.
+ */
+#define ALLOC_STALL_WARN_MSECS (10 * 1000UL)
+static unsigned long alloc_stall_warn_jiffies = INITIAL_JIFFIES;
+
 static bool page_contains_unaccepted(struct page *page, unsigned int order);
 static bool cond_accept_memory(struct zone *zone, unsigned int order,
 			       int alloc_flags);
@@ -4706,6 +4714,40 @@ check_retry_cpuset(int cpuset_mems_cookie, struct alloc_context *ac)
 	return false;
 }
 
+static void check_alloc_stall_warn(gfp_t gfp_mask, nodemask_t *nodemask,
+				unsigned int order, unsigned long alloc_start_time)
+{
+	static DEFINE_SPINLOCK(alloc_stall_lock);
+	unsigned long stall_msecs = jiffies_to_msecs(jiffies - alloc_start_time);
+
+	if (likely(stall_msecs < ALLOC_STALL_WARN_MSECS))
+		return;
+	if (time_is_after_jiffies(READ_ONCE(alloc_stall_warn_jiffies)))
+		return;
+	if (gfp_mask & __GFP_NOWARN)
+		return;
+
+	if (!spin_trylock(&alloc_stall_lock))
+		return;
+
+	/* Check again, this time under the lock */
+	if (time_is_after_jiffies(alloc_stall_warn_jiffies)) {
+		spin_unlock(&alloc_stall_lock);
+		return;
+	}
+
+	WRITE_ONCE(alloc_stall_warn_jiffies, jiffies + msecs_to_jiffies(ALLOC_STALL_WARN_MSECS));
+	spin_unlock(&alloc_stall_lock);
+
+	pr_warn("%s: page allocation stall for %lu secs: order:%d, mode:%#x(%pGg) nodemask=%*pbl",
+		current->comm, stall_msecs / MSEC_PER_SEC, order, gfp_mask, &gfp_mask,
+		nodemask_pr_args(nodemask));
+	cpuset_print_current_mems_allowed();
+	pr_cont("\n");
+	dump_stack();
+	warn_alloc_show_mem(gfp_mask, nodemask);
+}
+
 static inline struct page *
 __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
 						struct alloc_context *ac)
@@ -4726,6 +4768,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
 	int reserve_flags;
 	bool compact_first = false;
 	bool can_retry_reserves = true;
+	unsigned long alloc_start_time = jiffies;
 
 	if (unlikely(nofail)) {
 		/*
@@ -4841,6 +4884,9 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
 	if (current->flags & PF_MEMALLOC)
 		goto nopage;
 
+	/* If allocation has taken excessively long, warn about it */
+	check_alloc_stall_warn(gfp_mask, ac->nodemask, order, alloc_start_time);
+
 	/* Try direct reclaim and then allocating */
 	if (!compact_first) {
 		page = __alloc_pages_direct_reclaim(gfp_mask, order, alloc_flags,

On Mon 30-03-26 18:20:57, David Rientjes wrote:
> Previously, we had warnings when a single page allocation took longer
> than reasonably expected.  This was introduced in commit 63f53dea0c98
> ("mm: warn about allocations which stall for too long").
> 
> The warning was subsequently reverted in commit 400e22499dd9 ("mm: don't
> warn about allocations which stall for too long") because it was possible
> to generate memory pressure that would effectively stall further progress
> through printk execution.
> 
> Page allocation stalls in excess of 10 seconds are always useful to debug
> because they can result in severe userspace unresponsiveness.  Adding
> this artifact can be used to correlate with userspace going out to lunch
> and to understand the state of memory at the time.
> 
> There should be a reasonable expectation that this warning will never
> trigger given it is very passive, it will only be emitted when a page
> allocation takes longer than 10 seconds.  If it does trigger, this
> reveals an issue that should be fixed: a single page allocation should
> never loop for more than 10 seconds without oom killing to make memory
> available.
> 
> Unlike the original implementation, this implementation only reports
> stalls once for the system every 10 seconds.  Otherwise, many concurrent
> reclaimers could spam the kernel log unnecessarily.  Stalls are only
> reported when calling into direct reclaim.
> 
> Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
> Signed-off-by: David Rientjes <rientjes@google.com>

OK, let's go with this and tune it up as we find a need in the future.
Acked-by: Michal Hocko <mhocko@suse.com>
Thanks!
-- 
Michal Hocko
SUSE Labs

On Mon, Mar 30, 2026 at 06:20:57PM -0700, David Rientjes wrote:
> Previously, we had warnings when a single page allocation took longer
> than reasonably expected.  This was introduced in commit 63f53dea0c98
> ("mm: warn about allocations which stall for too long").
> 
> The warning was subsequently reverted in commit 400e22499dd9 ("mm: don't
> warn about allocations which stall for too long") because it was possible
> to generate memory pressure that would effectively stall further progress
> through printk execution.
> 
> Page allocation stalls in excess of 10 seconds are always useful to debug
> because they can result in severe userspace unresponsiveness.  Adding
> this artifact can be used to correlate with userspace going out to lunch
> and to understand the state of memory at the time.
> 
> There should be a reasonable expectation that this warning will never
> trigger given it is very passive, it will only be emitted when a page
> allocation takes longer than 10 seconds.  If it does trigger, this
> reveals an issue that should be fixed: a single page allocation should
> never loop for more than 10 seconds without oom killing to make memory
> available.
> 
> Unlike the original implementation, this implementation only reports
> stalls once for the system every 10 seconds.  Otherwise, many concurrent
> reclaimers could spam the kernel log unnecessarily.  Stalls are only
> reported when calling into direct reclaim.
> 
> Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
> Signed-off-by: David Rientjes <rientjes@google.com>

Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>

I am hoping that the reason you are reintroducing these warnings is
because you already are seeing such cases in your production
environment. Do you have anything interesting to share?