mm/migrate.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
When numa balancing is enabled with demotion, vmscan will call
migrate_pages when shrinking LRUs. Successful demotions will
cause node vmstat numbers to double-decrement, leading to an
imbalanced page count. The result is dmesg output like such:
$ cat /proc/sys/vm/stat_refresh
[77383.088417] vmstat_refresh: nr_isolated_anon -103212
[77383.088417] vmstat_refresh: nr_isolated_file -899642
This negative value may impact compaction and reclaim throttling.
The double-decrement occurs in the migrate_pages path:
caller to shrink_folio_list decrements the count
shrink_folio_list
demote_folio_list
migrate_pages
migrate_pages_batch
migrate_folio_move
migrate_folio_done
mod_node_page_state(-ve) <- second decrement
This path happens for SUCCESSFUL migrations, not failures. Typically
callers to migrate_pages are required to handle putback/accounting for
failures, but this is already handled in the shrink code.
When accounting for migrations, instead do not decrement the count
when the migration reason is MR_DEMOTION. As of v6.11, this demotion
logic is the only source of MR_DEMOTION.
Signed-off-by: Gregory Price <gourry@gourry.net>
Fixes: 26aa2d199d6f2 ("mm/migrate: demote pages during reclaim")
Cc: stable@vger.kernel.org
---
mm/migrate.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/migrate.c b/mm/migrate.c
index 923ea80ba744..e3aac274cf16 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1099,7 +1099,7 @@ static void migrate_folio_done(struct folio *src,
* not accounted to NR_ISOLATED_*. They can be recognized
* as __folio_test_movable
*/
- if (likely(!__folio_test_movable(src)))
+ if (likely(!__folio_test_movable(src)) && reason != MR_DEMOTION)
mod_node_page_state(folio_pgdat(src), NR_ISOLATED_ANON +
folio_is_file_lru(src), -folio_nr_pages(src));
--
2.43.0On Fri, Oct 25, 2024 at 10:17:24AM -0400, Gregory Price wrote:
> When numa balancing is enabled with demotion, vmscan will call
> migrate_pages when shrinking LRUs. Successful demotions will
> cause node vmstat numbers to double-decrement, leading to an
> imbalanced page count. The result is dmesg output like such:
>
> $ cat /proc/sys/vm/stat_refresh
>
> [77383.088417] vmstat_refresh: nr_isolated_anon -103212
> [77383.088417] vmstat_refresh: nr_isolated_file -899642
>
> This negative value may impact compaction and reclaim throttling.
>
> The double-decrement occurs in the migrate_pages path:
>
> caller to shrink_folio_list decrements the count
> shrink_folio_list
> demote_folio_list
> migrate_pages
> migrate_pages_batch
> migrate_folio_move
> migrate_folio_done
> mod_node_page_state(-ve) <- second decrement
>
> This path happens for SUCCESSFUL migrations, not failures. Typically
> callers to migrate_pages are required to handle putback/accounting for
> failures, but this is already handled in the shrink code.
>
> When accounting for migrations, instead do not decrement the count
> when the migration reason is MR_DEMOTION. As of v6.11, this demotion
> logic is the only source of MR_DEMOTION.
>
> Signed-off-by: Gregory Price <gourry@gourry.net>
> Fixes: 26aa2d199d6f2 ("mm/migrate: demote pages during reclaim")
> Cc: stable@vger.kernel.org
Reviewed-by: Oscar Salvador <osalvador@suse.de>
--
Oscar Salvador
SUSE Labs
On Fri, Oct 25, 2024 at 7:17 AM Gregory Price <gourry@gourry.net> wrote:
>
> When numa balancing is enabled with demotion, vmscan will call
> migrate_pages when shrinking LRUs. Successful demotions will
> cause node vmstat numbers to double-decrement, leading to an
> imbalanced page count. The result is dmesg output like such:
>
> $ cat /proc/sys/vm/stat_refresh
>
> [77383.088417] vmstat_refresh: nr_isolated_anon -103212
> [77383.088417] vmstat_refresh: nr_isolated_file -899642
>
> This negative value may impact compaction and reclaim throttling.
>
> The double-decrement occurs in the migrate_pages path:
>
> caller to shrink_folio_list decrements the count
> shrink_folio_list
> demote_folio_list
> migrate_pages
> migrate_pages_batch
> migrate_folio_move
> migrate_folio_done
> mod_node_page_state(-ve) <- second decrement
>
> This path happens for SUCCESSFUL migrations, not failures. Typically
> callers to migrate_pages are required to handle putback/accounting for
> failures, but this is already handled in the shrink code.
AFAIK, MGLRU doesn't dec/inc this counter, so it is not
double-decrement for MGLRU. Maybe "imbalance update" is better?
Anyway, it is just a nit. I'd suggest capturing the MGLRU case in the
commit log too.
>
> When accounting for migrations, instead do not decrement the count
> when the migration reason is MR_DEMOTION. As of v6.11, this demotion
> logic is the only source of MR_DEMOTION.
>
> Signed-off-by: Gregory Price <gourry@gourry.net>
> Fixes: 26aa2d199d6f2 ("mm/migrate: demote pages during reclaim")
> Cc: stable@vger.kernel.org
Thanks for catching this. Reviewed-by: Yang Shi <shy828301@gmail.com>
> ---
> mm/migrate.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 923ea80ba744..e3aac274cf16 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1099,7 +1099,7 @@ static void migrate_folio_done(struct folio *src,
> * not accounted to NR_ISOLATED_*. They can be recognized
> * as __folio_test_movable
> */
> - if (likely(!__folio_test_movable(src)))
> + if (likely(!__folio_test_movable(src)) && reason != MR_DEMOTION)
> mod_node_page_state(folio_pgdat(src), NR_ISOLATED_ANON +
> folio_is_file_lru(src), -folio_nr_pages(src));
>
> --
> 2.43.0
>
On Mon, Oct 28, 2024 at 01:45:48PM -0700, Yang Shi wrote:
> On Fri, Oct 25, 2024 at 7:17 AM Gregory Price <gourry@gourry.net> wrote:
> >
> > When numa balancing is enabled with demotion, vmscan will call
> > migrate_pages when shrinking LRUs. Successful demotions will
> > cause node vmstat numbers to double-decrement, leading to an
> > imbalanced page count. The result is dmesg output like such:
> >
> > $ cat /proc/sys/vm/stat_refresh
> >
> > [77383.088417] vmstat_refresh: nr_isolated_anon -103212
> > [77383.088417] vmstat_refresh: nr_isolated_file -899642
> >
> > This negative value may impact compaction and reclaim throttling.
> >
> > The double-decrement occurs in the migrate_pages path:
> >
> > caller to shrink_folio_list decrements the count
> > shrink_folio_list
> > demote_folio_list
> > migrate_pages
> > migrate_pages_batch
> > migrate_folio_move
> > migrate_folio_done
> > mod_node_page_state(-ve) <- second decrement
> >
> > This path happens for SUCCESSFUL migrations, not failures. Typically
> > callers to migrate_pages are required to handle putback/accounting for
> > failures, but this is already handled in the shrink code.
>
> AFAIK, MGLRU doesn't dec/inc this counter, so it is not
> double-decrement for MGLRU. Maybe "imbalance update" is better?
> Anyway, it is just a nit. I'd suggest capturing the MGLRU case in the
> commit log too.
>
Gotcha, so yeah saying it's an imbalance fix is more accurate.
So more accurate changelog is:
[PATCH] vmscan,migrate: fix page count imbalance on node stats when demoting pages
When numa balancing is enabled with demotion, vmscan will call
migrate_pages when shrinking LRUs. migrate_pages will decrement the
the node's isolated page count, leading to an imbalanced count when
invoked from (MG)LRU code.
The result is dmesg output like such:
$ cat /proc/sys/vm/stat_refresh
[77383.088417] vmstat_refresh: nr_isolated_anon -103212
[77383.088417] vmstat_refresh: nr_isolated_file -899642
This negative value may impact compaction and reclaim throttling.
The following path produces the decrement:
shrink_folio_list
demote_folio_list
migrate_pages
migrate_pages_batch
migrate_folio_move
migrate_folio_done
mod_node_page_state(-ve) <- decrement
This path happens for SUCCESSFUL migrations, not failures. Typically
callers to migrate_pages are required to handle putback/accounting for
failures, but this is already handled in the shrink code.
When accounting for migrations, instead do not decrement the count
when the migration reason is MR_DEMOTION. As of v6.11, this demotion
logic is the only source of MR_DEMOTION.
> >
> > Signed-off-by: Gregory Price <gourry@gourry.net>
> > Fixes: 26aa2d199d6f2 ("mm/migrate: demote pages during reclaim")
> > Cc: stable@vger.kernel.org
>
> Thanks for catching this. Reviewed-by: Yang Shi <shy828301@gmail.com>
>
> > ---
> > mm/migrate.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/mm/migrate.c b/mm/migrate.c
> > index 923ea80ba744..e3aac274cf16 100644
> > --- a/mm/migrate.c
> > +++ b/mm/migrate.c
> > @@ -1099,7 +1099,7 @@ static void migrate_folio_done(struct folio *src,
> > * not accounted to NR_ISOLATED_*. They can be recognized
> > * as __folio_test_movable
> > */
> > - if (likely(!__folio_test_movable(src)))
> > + if (likely(!__folio_test_movable(src)) && reason != MR_DEMOTION)
> > mod_node_page_state(folio_pgdat(src), NR_ISOLATED_ANON +
> > folio_is_file_lru(src), -folio_nr_pages(src));
> >
> > --
> > 2.43.0
> >
Gregory Price <gourry@gourry.net> writes:
> On Mon, Oct 28, 2024 at 01:45:48PM -0700, Yang Shi wrote:
>> On Fri, Oct 25, 2024 at 7:17 AM Gregory Price <gourry@gourry.net> wrote:
>> >
>> > When numa balancing is enabled with demotion, vmscan will call
>> > migrate_pages when shrinking LRUs. Successful demotions will
>> > cause node vmstat numbers to double-decrement, leading to an
>> > imbalanced page count. The result is dmesg output like such:
>> >
>> > $ cat /proc/sys/vm/stat_refresh
>> >
>> > [77383.088417] vmstat_refresh: nr_isolated_anon -103212
>> > [77383.088417] vmstat_refresh: nr_isolated_file -899642
>> >
>> > This negative value may impact compaction and reclaim throttling.
>> >
>> > The double-decrement occurs in the migrate_pages path:
>> >
>> > caller to shrink_folio_list decrements the count
>> > shrink_folio_list
>> > demote_folio_list
>> > migrate_pages
>> > migrate_pages_batch
>> > migrate_folio_move
>> > migrate_folio_done
>> > mod_node_page_state(-ve) <- second decrement
>> >
>> > This path happens for SUCCESSFUL migrations, not failures. Typically
>> > callers to migrate_pages are required to handle putback/accounting for
>> > failures, but this is already handled in the shrink code.
>>
>> AFAIK, MGLRU doesn't dec/inc this counter, so it is not
>> double-decrement for MGLRU. Maybe "imbalance update" is better?
>> Anyway, it is just a nit. I'd suggest capturing the MGLRU case in the
>> commit log too.
>>
>
> Gotcha, so yeah saying it's an imbalance fix is more accurate.
>
> So more accurate changelog is:
>
>
> [PATCH] vmscan,migrate: fix page count imbalance on node stats when demoting pages
>
> When numa balancing is enabled with demotion, vmscan will call
> migrate_pages when shrinking LRUs. migrate_pages will decrement the
> the node's isolated page count, leading to an imbalanced count when
> invoked from (MG)LRU code.
>
> The result is dmesg output like such:
>
> $ cat /proc/sys/vm/stat_refresh
>
> [77383.088417] vmstat_refresh: nr_isolated_anon -103212
> [77383.088417] vmstat_refresh: nr_isolated_file -899642
> This negative value may impact compaction and reclaim throttling.
>
> The following path produces the decrement:
>
> shrink_folio_list
> demote_folio_list
> migrate_pages
> migrate_pages_batch
> migrate_folio_move
> migrate_folio_done
> mod_node_page_state(-ve) <- decrement
I think that it may be better to mention the different behavior of LRU
and MGLRU. But that's not a big deal, change it again only if you think
it's necessary.
--
Best Regards,
Huang, Ying
> This path happens for SUCCESSFUL migrations, not failures. Typically
> callers to migrate_pages are required to handle putback/accounting for
> failures, but this is already handled in the shrink code.
>
> When accounting for migrations, instead do not decrement the count
> when the migration reason is MR_DEMOTION. As of v6.11, this demotion
> logic is the only source of MR_DEMOTION.
>
>
>> >
>> > Signed-off-by: Gregory Price <gourry@gourry.net>
>> > Fixes: 26aa2d199d6f2 ("mm/migrate: demote pages during reclaim")
>> > Cc: stable@vger.kernel.org
>>
>> Thanks for catching this. Reviewed-by: Yang Shi <shy828301@gmail.com>
>>
>> > ---
>> > mm/migrate.c | 2 +-
>> > 1 file changed, 1 insertion(+), 1 deletion(-)
>> >
>> > diff --git a/mm/migrate.c b/mm/migrate.c
>> > index 923ea80ba744..e3aac274cf16 100644
>> > --- a/mm/migrate.c
>> > +++ b/mm/migrate.c
>> > @@ -1099,7 +1099,7 @@ static void migrate_folio_done(struct folio *src,
>> > * not accounted to NR_ISOLATED_*. They can be recognized
>> > * as __folio_test_movable
>> > */
>> > - if (likely(!__folio_test_movable(src)))
>> > + if (likely(!__folio_test_movable(src)) && reason != MR_DEMOTION)
>> > mod_node_page_state(folio_pgdat(src), NR_ISOLATED_ANON +
>> > folio_is_file_lru(src), -folio_nr_pages(src));
>> >
>> > --
>> > 2.43.0
>> >
On Tue, Oct 29, 2024 at 08:34:34AM +0800, Huang, Ying wrote: > Gregory Price <gourry@gourry.net> writes: > > > On Mon, Oct 28, 2024 at 01:45:48PM -0700, Yang Shi wrote: > >> On Fri, Oct 25, 2024 at 7:17 AM Gregory Price <gourry@gourry.net> wrote: > >> > > >> > This path happens for SUCCESSFUL migrations, not failures. Typically > >> > callers to migrate_pages are required to handle putback/accounting for > >> > failures, but this is already handled in the shrink code. > >> > >> AFAIK, MGLRU doesn't dec/inc this counter, so it is not > >> double-decrement for MGLRU. Maybe "imbalance update" is better? > >> Anyway, it is just a nit. I'd suggest capturing the MGLRU case in the > >> commit log too. > >> > > > > Gotcha, so yeah saying it's an imbalance fix is more accurate. > > > > So more accurate changelog is: ... > > I think that it may be better to mention the different behavior of LRU > and MGLRU. But that's not a big deal, change it again only if you think > it's necessary. > The behavior isn't really different. It's either way migrate_pages decrements when it shouldn't going through the shink code - and both LRU and MGLRU go through the same code. That LRU does an inc/dec pair is irrelevant - neither should do the decrement in the migrate path. ~Gregory
On Fri, 25 Oct 2024, Gregory Price wrote:
>When numa balancing is enabled with demotion, vmscan will call
>migrate_pages when shrinking LRUs. Successful demotions will
>cause node vmstat numbers to double-decrement, leading to an
>imbalanced page count. The result is dmesg output like such:
>
>$ cat /proc/sys/vm/stat_refresh
>
>[77383.088417] vmstat_refresh: nr_isolated_anon -103212
>[77383.088417] vmstat_refresh: nr_isolated_file -899642
>
>This negative value may impact compaction and reclaim throttling.
>
>The double-decrement occurs in the migrate_pages path:
>
>caller to shrink_folio_list decrements the count
> shrink_folio_list
> demote_folio_list
> migrate_pages
> migrate_pages_batch
> migrate_folio_move
> migrate_folio_done
> mod_node_page_state(-ve) <- second decrement
>
>This path happens for SUCCESSFUL migrations, not failures. Typically
>callers to migrate_pages are required to handle putback/accounting for
>failures, but this is already handled in the shrink code.
>
>When accounting for migrations, instead do not decrement the count
>when the migration reason is MR_DEMOTION. As of v6.11, this demotion
>logic is the only source of MR_DEMOTION.
>
>Signed-off-by: Gregory Price <gourry@gourry.net>
>Fixes: 26aa2d199d6f2 ("mm/migrate: demote pages during reclaim")
>Cc: stable@vger.kernel.org
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
On Fri, Oct 25, 2024 at 10:17:24AM GMT, Gregory Price wrote:
> When numa balancing is enabled with demotion, vmscan will call
> migrate_pages when shrinking LRUs. Successful demotions will
> cause node vmstat numbers to double-decrement, leading to an
> imbalanced page count. The result is dmesg output like such:
>
> $ cat /proc/sys/vm/stat_refresh
>
> [77383.088417] vmstat_refresh: nr_isolated_anon -103212
> [77383.088417] vmstat_refresh: nr_isolated_file -899642
>
> This negative value may impact compaction and reclaim throttling.
>
> The double-decrement occurs in the migrate_pages path:
>
> caller to shrink_folio_list decrements the count
> shrink_folio_list
> demote_folio_list
> migrate_pages
> migrate_pages_batch
> migrate_folio_move
> migrate_folio_done
> mod_node_page_state(-ve) <- second decrement
>
> This path happens for SUCCESSFUL migrations, not failures. Typically
> callers to migrate_pages are required to handle putback/accounting for
> failures, but this is already handled in the shrink code.
>
> When accounting for migrations, instead do not decrement the count
> when the migration reason is MR_DEMOTION. As of v6.11, this demotion
> logic is the only source of MR_DEMOTION.
>
> Signed-off-by: Gregory Price <gourry@gourry.net>
> Fixes: 26aa2d199d6f2 ("mm/migrate: demote pages during reclaim")
> Cc: stable@vger.kernel.org
Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
This patch looks good for stable backports. For future I wonder if
instead of migrate_pages(), the caller providing the isolated folios,
manages the isolated stats (increments and decrements) similar to how
reclaim does it.
> ---
> mm/migrate.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 923ea80ba744..e3aac274cf16 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1099,7 +1099,7 @@ static void migrate_folio_done(struct folio *src,
> * not accounted to NR_ISOLATED_*. They can be recognized
> * as __folio_test_movable
> */
> - if (likely(!__folio_test_movable(src)))
> + if (likely(!__folio_test_movable(src)) && reason != MR_DEMOTION)
> mod_node_page_state(folio_pgdat(src), NR_ISOLATED_ANON +
> folio_is_file_lru(src), -folio_nr_pages(src));
>
> --
> 2.43.0
>
On Sun, Oct 27, 2024 at 10:24:10PM -0700, Shakeel Butt wrote:
> On Fri, Oct 25, 2024 at 10:17:24AM GMT, Gregory Price wrote:
> > When numa balancing is enabled with demotion, vmscan will call
> > migrate_pages when shrinking LRUs. Successful demotions will
> > cause node vmstat numbers to double-decrement, leading to an
> > imbalanced page count. The result is dmesg output like such:
> >
> > $ cat /proc/sys/vm/stat_refresh
> >
> > [77383.088417] vmstat_refresh: nr_isolated_anon -103212
> > [77383.088417] vmstat_refresh: nr_isolated_file -899642
> >
> > This negative value may impact compaction and reclaim throttling.
> >
> > The double-decrement occurs in the migrate_pages path:
> >
> > caller to shrink_folio_list decrements the count
> > shrink_folio_list
> > demote_folio_list
> > migrate_pages
> > migrate_pages_batch
> > migrate_folio_move
> > migrate_folio_done
> > mod_node_page_state(-ve) <- second decrement
> >
> > This path happens for SUCCESSFUL migrations, not failures. Typically
> > callers to migrate_pages are required to handle putback/accounting for
> > failures, but this is already handled in the shrink code.
> >
> > When accounting for migrations, instead do not decrement the count
> > when the migration reason is MR_DEMOTION. As of v6.11, this demotion
> > logic is the only source of MR_DEMOTION.
> >
> > Signed-off-by: Gregory Price <gourry@gourry.net>
> > Fixes: 26aa2d199d6f2 ("mm/migrate: demote pages during reclaim")
> > Cc: stable@vger.kernel.org
>
> Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
>
> This patch looks good for stable backports. For future I wonder if
> instead of migrate_pages(), the caller providing the isolated folios,
> manages the isolated stats (increments and decrements) similar to how
> reclaim does it.
>
Note that even if you provided the folios, you'd likely still end up in
migrate_pages_batch/migrate_folio_move and subsequently the same accounting
path. Probably there's some refactoring we can do to make the accounting
more obvious - it is very subtle here.
> > ---
> > mm/migrate.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/mm/migrate.c b/mm/migrate.c
> > index 923ea80ba744..e3aac274cf16 100644
> > --- a/mm/migrate.c
> > +++ b/mm/migrate.c
> > @@ -1099,7 +1099,7 @@ static void migrate_folio_done(struct folio *src,
> > * not accounted to NR_ISOLATED_*. They can be recognized
> > * as __folio_test_movable
> > */
> > - if (likely(!__folio_test_movable(src)))
> > + if (likely(!__folio_test_movable(src)) && reason != MR_DEMOTION)
> > mod_node_page_state(folio_pgdat(src), NR_ISOLATED_ANON +
> > folio_is_file_lru(src), -folio_nr_pages(src));
> >
> > --
> > 2.43.0
> >
Gregory Price <gourry@gourry.net> writes:
> On Sun, Oct 27, 2024 at 10:24:10PM -0700, Shakeel Butt wrote:
>> On Fri, Oct 25, 2024 at 10:17:24AM GMT, Gregory Price wrote:
>> > When numa balancing is enabled with demotion, vmscan will call
>> > migrate_pages when shrinking LRUs. Successful demotions will
>> > cause node vmstat numbers to double-decrement, leading to an
>> > imbalanced page count. The result is dmesg output like such:
>> >
>> > $ cat /proc/sys/vm/stat_refresh
>> >
>> > [77383.088417] vmstat_refresh: nr_isolated_anon -103212
>> > [77383.088417] vmstat_refresh: nr_isolated_file -899642
>> >
>> > This negative value may impact compaction and reclaim throttling.
>> >
>> > The double-decrement occurs in the migrate_pages path:
>> >
>> > caller to shrink_folio_list decrements the count
>> > shrink_folio_list
>> > demote_folio_list
>> > migrate_pages
>> > migrate_pages_batch
>> > migrate_folio_move
>> > migrate_folio_done
>> > mod_node_page_state(-ve) <- second decrement
>> >
>> > This path happens for SUCCESSFUL migrations, not failures. Typically
>> > callers to migrate_pages are required to handle putback/accounting for
>> > failures, but this is already handled in the shrink code.
>> >
>> > When accounting for migrations, instead do not decrement the count
>> > when the migration reason is MR_DEMOTION. As of v6.11, this demotion
>> > logic is the only source of MR_DEMOTION.
>> >
>> > Signed-off-by: Gregory Price <gourry@gourry.net>
>> > Fixes: 26aa2d199d6f2 ("mm/migrate: demote pages during reclaim")
>> > Cc: stable@vger.kernel.org
>>
>> Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
>>
>> This patch looks good for stable backports. For future I wonder if
>> instead of migrate_pages(), the caller providing the isolated folios,
>> manages the isolated stats (increments and decrements) similar to how
>> reclaim does it.
>>
>
> Note that even if you provided the folios, you'd likely still end up in
> migrate_pages_batch/migrate_folio_move and subsequently the same accounting
> path. Probably there's some refactoring we can do to make the accounting
> more obvious - it is very subtle here.
I agree with Shakeel here. It's better for the caller who isolates the
folios to increase and decrease the isolation counter. And yes, some
refactoring is required.
--
Best Regards,
Huang, Ying
>> > ---
>> > mm/migrate.c | 2 +-
>> > 1 file changed, 1 insertion(+), 1 deletion(-)
>> >
>> > diff --git a/mm/migrate.c b/mm/migrate.c
>> > index 923ea80ba744..e3aac274cf16 100644
>> > --- a/mm/migrate.c
>> > +++ b/mm/migrate.c
>> > @@ -1099,7 +1099,7 @@ static void migrate_folio_done(struct folio *src,
>> > * not accounted to NR_ISOLATED_*. They can be recognized
>> > * as __folio_test_movable
>> > */
>> > - if (likely(!__folio_test_movable(src)))
>> > + if (likely(!__folio_test_movable(src)) && reason != MR_DEMOTION)
>> > mod_node_page_state(folio_pgdat(src), NR_ISOLATED_ANON +
>> > folio_is_file_lru(src), -folio_nr_pages(src));
>> >
>> > --
>> > 2.43.0
>> >
Gregory Price <gourry@gourry.net> writes:
> When numa balancing is enabled with demotion, vmscan will call
> migrate_pages when shrinking LRUs. Successful demotions will
> cause node vmstat numbers to double-decrement, leading to an
> imbalanced page count. The result is dmesg output like such:
>
> $ cat /proc/sys/vm/stat_refresh
>
> [77383.088417] vmstat_refresh: nr_isolated_anon -103212
> [77383.088417] vmstat_refresh: nr_isolated_file -899642
>
> This negative value may impact compaction and reclaim throttling.
>
> The double-decrement occurs in the migrate_pages path:
>
> caller to shrink_folio_list decrements the count
> shrink_folio_list
> demote_folio_list
> migrate_pages
> migrate_pages_batch
> migrate_folio_move
> migrate_folio_done
> mod_node_page_state(-ve) <- second decrement
>
> This path happens for SUCCESSFUL migrations, not failures. Typically
> callers to migrate_pages are required to handle putback/accounting for
> failures, but this is already handled in the shrink code.
>
> When accounting for migrations, instead do not decrement the count
> when the migration reason is MR_DEMOTION. As of v6.11, this demotion
> logic is the only source of MR_DEMOTION.
>
> Signed-off-by: Gregory Price <gourry@gourry.net>
> Fixes: 26aa2d199d6f2 ("mm/migrate: demote pages during reclaim")
> Cc: stable@vger.kernel.org
> ---
> mm/migrate.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 923ea80ba744..e3aac274cf16 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1099,7 +1099,7 @@ static void migrate_folio_done(struct folio *src,
> * not accounted to NR_ISOLATED_*. They can be recognized
> * as __folio_test_movable
> */
> - if (likely(!__folio_test_movable(src)))
> + if (likely(!__folio_test_movable(src)) && reason != MR_DEMOTION)
> mod_node_page_state(folio_pgdat(src), NR_ISOLATED_ANON +
> folio_is_file_lru(src), -folio_nr_pages(src));
Good catch! Thanks for doing this! Feel free to add
Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
in the future versions.
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