From: Michal Hocko <mhocko@suse.com>
There is no existing user of the flag and the flag is dangerous because
a nested allocation context can use GFP_NOFAIL which could cause
unexpected failure. Such a code would be hard to maintain because it
could be deeper in the call chain.
PF_MEMALLOC_NORECLAIM has been added even when it was pointed out [1]
that such a allocation contex is inherently unsafe if the context
doesn't fully control all allocations called from this context.
[1] https://lore.kernel.org/all/ZcM0xtlKbAOFjv5n@tiehlicka/
Signed-off-by: Michal Hocko <mhocko@suse.com>
---
include/linux/sched.h | 1 -
include/linux/sched/mm.h | 7 ++-----
2 files changed, 2 insertions(+), 6 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index f8d150343d42..72dad3a6317a 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1657,7 +1657,6 @@ extern struct pid *cad_pid;
* I am cleaning dirty pages from some other bdi. */
#define PF_KTHREAD 0x00200000 /* I am a kernel thread */
#define PF_RANDOMIZE 0x00400000 /* Randomize virtual address space */
-#define PF_MEMALLOC_NORECLAIM 0x00800000 /* All allocation requests will clear __GFP_DIRECT_RECLAIM */
#define PF_MEMALLOC_NOWARN 0x01000000 /* All allocation requests will inherit __GFP_NOWARN */
#define PF__HOLE__02000000 0x02000000
#define PF_NO_SETAFFINITY 0x04000000 /* Userland is not allowed to meddle with cpus_mask */
diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
index 91546493c43d..c49f2b24acb9 100644
--- a/include/linux/sched/mm.h
+++ b/include/linux/sched/mm.h
@@ -260,16 +260,13 @@ static inline gfp_t current_gfp_context(gfp_t flags)
if (unlikely(pflags & (PF_MEMALLOC_NOIO |
PF_MEMALLOC_NOFS |
- PF_MEMALLOC_NORECLAIM |
PF_MEMALLOC_NOWARN |
PF_MEMALLOC_PIN))) {
/*
* Stronger flags before weaker flags:
- * NORECLAIM implies NOIO, which in turn implies NOFS
+ * NOIO implies NOFS
*/
- if (pflags & PF_MEMALLOC_NORECLAIM)
- flags &= ~__GFP_DIRECT_RECLAIM;
- else if (pflags & PF_MEMALLOC_NOIO)
+ if (pflags & PF_MEMALLOC_NOIO)
flags &= ~(__GFP_IO | __GFP_FS);
else if (pflags & PF_MEMALLOC_NOFS)
flags &= ~__GFP_FS;
--
2.46.0Looks good: Reviewed-by: Christoph Hellwig <hch@lst.de>
On Mon, Aug 26, 2024 at 10:47:13AM GMT, Michal Hocko wrote: > From: Michal Hocko <mhocko@suse.com> > > There is no existing user of the flag and the flag is dangerous because > a nested allocation context can use GFP_NOFAIL which could cause > unexpected failure. Such a code would be hard to maintain because it > could be deeper in the call chain. > > PF_MEMALLOC_NORECLAIM has been added even when it was pointed out [1] > that such a allocation contex is inherently unsafe if the context > doesn't fully control all allocations called from this context. I don't really buy the unsafety argument; if it applies to anything, it applies to GFP_NOFAIL - but we recently grew warnings about unsafe uses for it, so I don't see it as a great concern. GFP_NORECLAIM is frequently desirable as a hint about the latency requirements of a codepath; "don't try too hard, I've got fallbacks and I'm in a codepath where I don't want to block too long". I expect PF_MEMALLOC_NORECLAIM will find legitimate uses.
On Mon, Aug 26, 2024 at 10:47:13AM +0200, Michal Hocko wrote: > From: Michal Hocko <mhocko@suse.com> > > There is no existing user of the flag and the flag is dangerous because > a nested allocation context can use GFP_NOFAIL which could cause > unexpected failure. Such a code would be hard to maintain because it > could be deeper in the call chain. > > PF_MEMALLOC_NORECLAIM has been added even when it was pointed out [1] > that such a allocation contex is inherently unsafe if the context > doesn't fully control all allocations called from this context. Wouldn't a straight-up revert of eab0af905bfc be cleaner? Or is there a reason to keep PF_MEMALLOC_NOWARN?
On Mon 26-08-24 14:59:29, Matthew Wilcox wrote: > On Mon, Aug 26, 2024 at 10:47:13AM +0200, Michal Hocko wrote: > > From: Michal Hocko <mhocko@suse.com> > > > > There is no existing user of the flag and the flag is dangerous because > > a nested allocation context can use GFP_NOFAIL which could cause > > unexpected failure. Such a code would be hard to maintain because it > > could be deeper in the call chain. > > > > PF_MEMALLOC_NORECLAIM has been added even when it was pointed out [1] > > that such a allocation contex is inherently unsafe if the context > > doesn't fully control all allocations called from this context. > > Wouldn't a straight-up revert of eab0af905bfc be cleaner? Or is there > a reason to keep PF_MEMALLOC_NOWARN? I wanted to make it PF_MEMALLOC_NORECLAIM specific. I do not have a strong case against PF_MEMALLOC_NOWARN TBH. It is a hack because the scope is claiming something about all allocations within the scope without necessarily knowing all of them (including potential future changes). But NOWARN is not really harmful so I do not care strongly. If a plan revert is preferably, I will go with it. -- Michal Hocko SUSE Labs
On Mon, Aug 26, 2024 at 06:51:55PM +0200, Michal Hocko wrote: > On Mon 26-08-24 14:59:29, Matthew Wilcox wrote: > > On Mon, Aug 26, 2024 at 10:47:13AM +0200, Michal Hocko wrote: > > > From: Michal Hocko <mhocko@suse.com> > > > > > > There is no existing user of the flag and the flag is dangerous because > > > a nested allocation context can use GFP_NOFAIL which could cause > > > unexpected failure. Such a code would be hard to maintain because it > > > could be deeper in the call chain. > > > > > > PF_MEMALLOC_NORECLAIM has been added even when it was pointed out [1] > > > that such a allocation contex is inherently unsafe if the context > > > doesn't fully control all allocations called from this context. > > > > Wouldn't a straight-up revert of eab0af905bfc be cleaner? Or is there > > a reason to keep PF_MEMALLOC_NOWARN? > > I wanted to make it PF_MEMALLOC_NORECLAIM specific. I do not have a > strong case against PF_MEMALLOC_NOWARN TBH. It is a hack because the > scope is claiming something about all allocations within the scope > without necessarily knowing all of them (including potential future > changes). But NOWARN is not really harmful so I do not care strongly. > > If a plan revert is preferably, I will go with it. There aren't any other users of PF_MEMALLOC_NOWARN and it definitely seems like something you want at a callsite rather than blanket for every allocation below this point. We don't seem to have many PF_ flags left, so let's not keep it around if there's no immediate plans for it.
On Mon 26-08-24 18:49:23, Matthew Wilcox wrote:
> On Mon, Aug 26, 2024 at 06:51:55PM +0200, Michal Hocko wrote:
[...]
> > If a plan revert is preferably, I will go with it.
>
> There aren't any other users of PF_MEMALLOC_NOWARN and it definitely
> seems like something you want at a callsite rather than blanket for every
> allocation below this point. We don't seem to have many PF_ flags left,
> so let's not keep it around if there's no immediate plans for it.
Good point. What about this?
---
From 923cd429d4b1a3520c93bcf46611ae74a3158865 Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@suse.com>
Date: Mon, 26 Aug 2024 21:15:02 +0200
Subject: [PATCH] Revert "mm: introduce PF_MEMALLOC_NORECLAIM,
PF_MEMALLOC_NOWARN"
This reverts commit eab0af905bfc3e9c05da2ca163d76a1513159aa4.
There is no existing user of those flags. PF_MEMALLOC_NOWARN is
dangerous because a nested allocation context can use GFP_NOFAIL which
could cause unexpected failure. Such a code would be hard to maintain
because it could be deeper in the call chain.
PF_MEMALLOC_NORECLAIM has been added even when it was pointed out [1]
that such a allocation contex is inherently unsafe if the context
doesn't fully control all allocations called from this context.
While PF_MEMALLOC_NOWARN is not dangerous the way PF_MEMALLOC_NORECLAIM
is it doesn't have any user and as Matthew has pointed out we are
running out of those flags so better reclaim it without any real users.
[1] https://lore.kernel.org/all/ZcM0xtlKbAOFjv5n@tiehlicka/
Signed-off-by: Michal Hocko <mhocko@suse.com>
---
include/linux/sched.h | 4 ++--
include/linux/sched/mm.h | 17 ++++-------------
2 files changed, 6 insertions(+), 15 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index f8d150343d42..731ff1078c9e 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1657,8 +1657,8 @@ extern struct pid *cad_pid;
* I am cleaning dirty pages from some other bdi. */
#define PF_KTHREAD 0x00200000 /* I am a kernel thread */
#define PF_RANDOMIZE 0x00400000 /* Randomize virtual address space */
-#define PF_MEMALLOC_NORECLAIM 0x00800000 /* All allocation requests will clear __GFP_DIRECT_RECLAIM */
-#define PF_MEMALLOC_NOWARN 0x01000000 /* All allocation requests will inherit __GFP_NOWARN */
+#define PF__HOLE__00800000 0x00800000
+#define PF__HOLE__01000000 0x01000000
#define PF__HOLE__02000000 0x02000000
#define PF_NO_SETAFFINITY 0x04000000 /* Userland is not allowed to meddle with cpus_mask */
#define PF_MCE_EARLY 0x08000000 /* Early kill for mce process policy */
diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
index 91546493c43d..07c4fde32827 100644
--- a/include/linux/sched/mm.h
+++ b/include/linux/sched/mm.h
@@ -258,25 +258,16 @@ static inline gfp_t current_gfp_context(gfp_t flags)
{
unsigned int pflags = READ_ONCE(current->flags);
- if (unlikely(pflags & (PF_MEMALLOC_NOIO |
- PF_MEMALLOC_NOFS |
- PF_MEMALLOC_NORECLAIM |
- PF_MEMALLOC_NOWARN |
- PF_MEMALLOC_PIN))) {
+ if (unlikely(pflags & (PF_MEMALLOC_NOIO | PF_MEMALLOC_NOFS | PF_MEMALLOC_PIN))) {
/*
- * Stronger flags before weaker flags:
- * NORECLAIM implies NOIO, which in turn implies NOFS
+ * NOIO implies both NOIO and NOFS and it is a weaker context
+ * so always make sure it makes precedence
*/
- if (pflags & PF_MEMALLOC_NORECLAIM)
- flags &= ~__GFP_DIRECT_RECLAIM;
- else if (pflags & PF_MEMALLOC_NOIO)
+ if (pflags & PF_MEMALLOC_NOIO)
flags &= ~(__GFP_IO | __GFP_FS);
else if (pflags & PF_MEMALLOC_NOFS)
flags &= ~__GFP_FS;
- if (pflags & PF_MEMALLOC_NOWARN)
- flags |= __GFP_NOWARN;
-
if (pflags & PF_MEMALLOC_PIN)
flags &= ~__GFP_MOVABLE;
}
--
2.46.0
--
Michal Hocko
SUSE Labs
On 8/26/24 21:18, Michal Hocko wrote:
> On Mon 26-08-24 18:49:23, Matthew Wilcox wrote:
>> On Mon, Aug 26, 2024 at 06:51:55PM +0200, Michal Hocko wrote:
> [...]
>> > If a plan revert is preferably, I will go with it.
>>
>> There aren't any other users of PF_MEMALLOC_NOWARN and it definitely
>> seems like something you want at a callsite rather than blanket for every
>> allocation below this point. We don't seem to have many PF_ flags left,
>> so let's not keep it around if there's no immediate plans for it.
>
> Good point. What about this?
> ---
> From 923cd429d4b1a3520c93bcf46611ae74a3158865 Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@suse.com>
> Date: Mon, 26 Aug 2024 21:15:02 +0200
> Subject: [PATCH] Revert "mm: introduce PF_MEMALLOC_NORECLAIM,
> PF_MEMALLOC_NOWARN"
>
> This reverts commit eab0af905bfc3e9c05da2ca163d76a1513159aa4.
>
> There is no existing user of those flags. PF_MEMALLOC_NOWARN is
> dangerous because a nested allocation context can use GFP_NOFAIL which
> could cause unexpected failure. Such a code would be hard to maintain
> because it could be deeper in the call chain.
>
> PF_MEMALLOC_NORECLAIM has been added even when it was pointed out [1]
> that such a allocation contex is inherently unsafe if the context
> doesn't fully control all allocations called from this context.
>
> While PF_MEMALLOC_NOWARN is not dangerous the way PF_MEMALLOC_NORECLAIM
> is it doesn't have any user and as Matthew has pointed out we are
> running out of those flags so better reclaim it without any real users.
>
> [1] https://lore.kernel.org/all/ZcM0xtlKbAOFjv5n@tiehlicka/
>
> Signed-off-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
> ---
> include/linux/sched.h | 4 ++--
> include/linux/sched/mm.h | 17 ++++-------------
> 2 files changed, 6 insertions(+), 15 deletions(-)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index f8d150343d42..731ff1078c9e 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1657,8 +1657,8 @@ extern struct pid *cad_pid;
> * I am cleaning dirty pages from some other bdi. */
> #define PF_KTHREAD 0x00200000 /* I am a kernel thread */
> #define PF_RANDOMIZE 0x00400000 /* Randomize virtual address space */
> -#define PF_MEMALLOC_NORECLAIM 0x00800000 /* All allocation requests will clear __GFP_DIRECT_RECLAIM */
> -#define PF_MEMALLOC_NOWARN 0x01000000 /* All allocation requests will inherit __GFP_NOWARN */
> +#define PF__HOLE__00800000 0x00800000
> +#define PF__HOLE__01000000 0x01000000
> #define PF__HOLE__02000000 0x02000000
> #define PF_NO_SETAFFINITY 0x04000000 /* Userland is not allowed to meddle with cpus_mask */
> #define PF_MCE_EARLY 0x08000000 /* Early kill for mce process policy */
> diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> index 91546493c43d..07c4fde32827 100644
> --- a/include/linux/sched/mm.h
> +++ b/include/linux/sched/mm.h
> @@ -258,25 +258,16 @@ static inline gfp_t current_gfp_context(gfp_t flags)
> {
> unsigned int pflags = READ_ONCE(current->flags);
>
> - if (unlikely(pflags & (PF_MEMALLOC_NOIO |
> - PF_MEMALLOC_NOFS |
> - PF_MEMALLOC_NORECLAIM |
> - PF_MEMALLOC_NOWARN |
> - PF_MEMALLOC_PIN))) {
> + if (unlikely(pflags & (PF_MEMALLOC_NOIO | PF_MEMALLOC_NOFS | PF_MEMALLOC_PIN))) {
> /*
> - * Stronger flags before weaker flags:
> - * NORECLAIM implies NOIO, which in turn implies NOFS
> + * NOIO implies both NOIO and NOFS and it is a weaker context
> + * so always make sure it makes precedence
> */
> - if (pflags & PF_MEMALLOC_NORECLAIM)
> - flags &= ~__GFP_DIRECT_RECLAIM;
> - else if (pflags & PF_MEMALLOC_NOIO)
> + if (pflags & PF_MEMALLOC_NOIO)
> flags &= ~(__GFP_IO | __GFP_FS);
> else if (pflags & PF_MEMALLOC_NOFS)
> flags &= ~__GFP_FS;
>
> - if (pflags & PF_MEMALLOC_NOWARN)
> - flags |= __GFP_NOWARN;
> -
> if (pflags & PF_MEMALLOC_PIN)
> flags &= ~__GFP_MOVABLE;
> }
On Mon, Aug 26, 2024 at 09:18:01PM +0200, Michal Hocko wrote: > On Mon 26-08-24 18:49:23, Matthew Wilcox wrote: > > On Mon, Aug 26, 2024 at 06:51:55PM +0200, Michal Hocko wrote: > [...] > > > If a plan revert is preferably, I will go with it. > > > > There aren't any other users of PF_MEMALLOC_NOWARN and it definitely > > seems like something you want at a callsite rather than blanket for every > > allocation below this point. We don't seem to have many PF_ flags left, > > so let's not keep it around if there's no immediate plans for it. > > Good point. What about this? > --- > From 923cd429d4b1a3520c93bcf46611ae74a3158865 Mon Sep 17 00:00:00 2001 > From: Michal Hocko <mhocko@suse.com> > Date: Mon, 26 Aug 2024 21:15:02 +0200 > Subject: [PATCH] Revert "mm: introduce PF_MEMALLOC_NORECLAIM, > PF_MEMALLOC_NOWARN" > > This reverts commit eab0af905bfc3e9c05da2ca163d76a1513159aa4. > > There is no existing user of those flags. PF_MEMALLOC_NOWARN is > dangerous because a nested allocation context can use GFP_NOFAIL which > could cause unexpected failure. Such a code would be hard to maintain > because it could be deeper in the call chain. > > PF_MEMALLOC_NORECLAIM has been added even when it was pointed out [1] > that such a allocation contex is inherently unsafe if the context > doesn't fully control all allocations called from this context. > > While PF_MEMALLOC_NOWARN is not dangerous the way PF_MEMALLOC_NORECLAIM > is it doesn't have any user and as Matthew has pointed out we are > running out of those flags so better reclaim it without any real users. > > [1] https://lore.kernel.org/all/ZcM0xtlKbAOFjv5n@tiehlicka/ > > Signed-off-by: Michal Hocko <mhocko@suse.com> Looks good to me. Reviewed-by: Dave Chinner <dchinner@redhat.com> -- Dave Chinner david@fromorbit.com
On Mon, Aug 26, 2024 at 09:18:01PM +0200, Michal Hocko wrote:
> On Mon 26-08-24 18:49:23, Matthew Wilcox wrote:
> > On Mon, Aug 26, 2024 at 06:51:55PM +0200, Michal Hocko wrote:
> [...]
> > > If a plan revert is preferably, I will go with it.
> >
> > There aren't any other users of PF_MEMALLOC_NOWARN and it definitely
> > seems like something you want at a callsite rather than blanket for every
> > allocation below this point. We don't seem to have many PF_ flags left,
> > so let's not keep it around if there's no immediate plans for it.
>
> Good point. What about this?
Looks clean to me.
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> >From 923cd429d4b1a3520c93bcf46611ae74a3158865 Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@suse.com>
> Date: Mon, 26 Aug 2024 21:15:02 +0200
> Subject: [PATCH] Revert "mm: introduce PF_MEMALLOC_NORECLAIM,
> PF_MEMALLOC_NOWARN"
>
> This reverts commit eab0af905bfc3e9c05da2ca163d76a1513159aa4.
>
> There is no existing user of those flags. PF_MEMALLOC_NOWARN is
> dangerous because a nested allocation context can use GFP_NOFAIL which
> could cause unexpected failure. Such a code would be hard to maintain
> because it could be deeper in the call chain.
>
> PF_MEMALLOC_NORECLAIM has been added even when it was pointed out [1]
> that such a allocation contex is inherently unsafe if the context
> doesn't fully control all allocations called from this context.
>
> While PF_MEMALLOC_NOWARN is not dangerous the way PF_MEMALLOC_NORECLAIM
> is it doesn't have any user and as Matthew has pointed out we are
> running out of those flags so better reclaim it without any real users.
>
> [1] https://lore.kernel.org/all/ZcM0xtlKbAOFjv5n@tiehlicka/
>
> Signed-off-by: Michal Hocko <mhocko@suse.com>
> ---
> include/linux/sched.h | 4 ++--
> include/linux/sched/mm.h | 17 ++++-------------
> 2 files changed, 6 insertions(+), 15 deletions(-)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index f8d150343d42..731ff1078c9e 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1657,8 +1657,8 @@ extern struct pid *cad_pid;
> * I am cleaning dirty pages from some other bdi. */
> #define PF_KTHREAD 0x00200000 /* I am a kernel thread */
> #define PF_RANDOMIZE 0x00400000 /* Randomize virtual address space */
> -#define PF_MEMALLOC_NORECLAIM 0x00800000 /* All allocation requests will clear __GFP_DIRECT_RECLAIM */
> -#define PF_MEMALLOC_NOWARN 0x01000000 /* All allocation requests will inherit __GFP_NOWARN */
> +#define PF__HOLE__00800000 0x00800000
> +#define PF__HOLE__01000000 0x01000000
> #define PF__HOLE__02000000 0x02000000
> #define PF_NO_SETAFFINITY 0x04000000 /* Userland is not allowed to meddle with cpus_mask */
> #define PF_MCE_EARLY 0x08000000 /* Early kill for mce process policy */
> diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> index 91546493c43d..07c4fde32827 100644
> --- a/include/linux/sched/mm.h
> +++ b/include/linux/sched/mm.h
> @@ -258,25 +258,16 @@ static inline gfp_t current_gfp_context(gfp_t flags)
> {
> unsigned int pflags = READ_ONCE(current->flags);
>
> - if (unlikely(pflags & (PF_MEMALLOC_NOIO |
> - PF_MEMALLOC_NOFS |
> - PF_MEMALLOC_NORECLAIM |
> - PF_MEMALLOC_NOWARN |
> - PF_MEMALLOC_PIN))) {
> + if (unlikely(pflags & (PF_MEMALLOC_NOIO | PF_MEMALLOC_NOFS | PF_MEMALLOC_PIN))) {
> /*
> - * Stronger flags before weaker flags:
> - * NORECLAIM implies NOIO, which in turn implies NOFS
> + * NOIO implies both NOIO and NOFS and it is a weaker context
> + * so always make sure it makes precedence
> */
> - if (pflags & PF_MEMALLOC_NORECLAIM)
> - flags &= ~__GFP_DIRECT_RECLAIM;
> - else if (pflags & PF_MEMALLOC_NOIO)
> + if (pflags & PF_MEMALLOC_NOIO)
> flags &= ~(__GFP_IO | __GFP_FS);
> else if (pflags & PF_MEMALLOC_NOFS)
> flags &= ~__GFP_FS;
>
> - if (pflags & PF_MEMALLOC_NOWARN)
> - flags |= __GFP_NOWARN;
> -
> if (pflags & PF_MEMALLOC_PIN)
> flags &= ~__GFP_MOVABLE;
> }
> --
> 2.46.0
>
>
> --
> Michal Hocko
> SUSE Labs
On Mon, Aug 26, 2024 at 4:53 PM Michal Hocko <mhocko@kernel.org> wrote: > > From: Michal Hocko <mhocko@suse.com> > > There is no existing user of the flag and the flag is dangerous because > a nested allocation context can use GFP_NOFAIL which could cause > unexpected failure. Such a code would be hard to maintain because it > could be deeper in the call chain. > > PF_MEMALLOC_NORECLAIM has been added even when it was pointed out [1] > that such a allocation contex is inherently unsafe if the context > doesn't fully control all allocations called from this context. > > [1] https://lore.kernel.org/all/ZcM0xtlKbAOFjv5n@tiehlicka/ > > Signed-off-by: Michal Hocko <mhocko@suse.com> > --- > include/linux/sched.h | 1 - > include/linux/sched/mm.h | 7 ++----- > 2 files changed, 2 insertions(+), 6 deletions(-) > > diff --git a/include/linux/sched.h b/include/linux/sched.h > index f8d150343d42..72dad3a6317a 100644 > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -1657,7 +1657,6 @@ extern struct pid *cad_pid; > * I am cleaning dirty pages from some other bdi. */ > #define PF_KTHREAD 0x00200000 /* I am a kernel thread */ > #define PF_RANDOMIZE 0x00400000 /* Randomize virtual address space */ > -#define PF_MEMALLOC_NORECLAIM 0x00800000 /* All allocation requests will clear __GFP_DIRECT_RECLAIM */ To maintain consistency with the other unused bits, it would be better to define PF__HOLE__00800000 instead. -- Regards Yafang
On Mon 26-08-24 21:48:34, Yafang Shao wrote: > On Mon, Aug 26, 2024 at 4:53 PM Michal Hocko <mhocko@kernel.org> wrote: > > > > From: Michal Hocko <mhocko@suse.com> > > > > There is no existing user of the flag and the flag is dangerous because > > a nested allocation context can use GFP_NOFAIL which could cause > > unexpected failure. Such a code would be hard to maintain because it > > could be deeper in the call chain. > > > > PF_MEMALLOC_NORECLAIM has been added even when it was pointed out [1] > > that such a allocation contex is inherently unsafe if the context > > doesn't fully control all allocations called from this context. > > > > [1] https://lore.kernel.org/all/ZcM0xtlKbAOFjv5n@tiehlicka/ > > > > Signed-off-by: Michal Hocko <mhocko@suse.com> > > --- > > include/linux/sched.h | 1 - > > include/linux/sched/mm.h | 7 ++----- > > 2 files changed, 2 insertions(+), 6 deletions(-) > > > > diff --git a/include/linux/sched.h b/include/linux/sched.h > > index f8d150343d42..72dad3a6317a 100644 > > --- a/include/linux/sched.h > > +++ b/include/linux/sched.h > > @@ -1657,7 +1657,6 @@ extern struct pid *cad_pid; > > * I am cleaning dirty pages from some other bdi. */ > > #define PF_KTHREAD 0x00200000 /* I am a kernel thread */ > > #define PF_RANDOMIZE 0x00400000 /* Randomize virtual address space */ > > -#define PF_MEMALLOC_NORECLAIM 0x00800000 /* All allocation requests will clear __GFP_DIRECT_RECLAIM */ > > To maintain consistency with the other unused bits, it would be better > to define PF__HOLE__00800000 instead. OK -- Michal Hocko SUSE Labs
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