Upon running some proactive reclaim tests using memory.reclaim, we
noticed some tests flaking where writing to memory.reclaim would be
successful even though we did not reclaim the requested amount fully.
Looking further into it, I discovered that *sometimes* we over-report
the number of reclaimed pages in memcg reclaim.
Reclaimed pages through other means than LRU-based reclaim are tracked
through reclaim_state in struct scan_control, which is stashed in
current task_struct. These pages are added to the number of reclaimed
pages through LRUs. For memcg reclaim, these pages generally cannot be
linked to the memcg under reclaim and can cause an overestimated count
of reclaimed pages. This short series tries to address that.
Patch 1 ignores pages reclaimed outside of LRU reclaim in memcg reclaim.
The pages are uncharged anyway, so even if we end up under-reporting
reclaimed pages we will still succeed in making progress during
charging.
Patch 2 is just refactoring, it adds helpers that wrap some
operations on current->reclaim_state, and rename
reclaim_state->reclaimed_slab to reclaim_state->reclaimed. It also adds
a huge comment explaining why we ignore pages reclaimed outside of LRU
reclaim in memcg reclaim.
The patches are divided as such so that patch 1 can be easily backported
without all the refactoring noise.
v4 -> v5:
- Separate the functional fix into its own patch, and squash all the
refactoring into a single second patch for ease of backporting (Andrew
Morton).
v4: https://lore.kernel.org/lkml/[email protected]/
Yosry Ahmed (2):
mm: vmscan: ignore non-LRU-based reclaim in memcg reclaim
mm: vmscan: refactor reclaim_state helpers
fs/inode.c | 3 +-
fs/xfs/xfs_buf.c | 3 +-
include/linux/swap.h | 17 ++++++++++-
mm/slab.c | 3 +-
mm/slob.c | 6 ++--
mm/slub.c | 5 ++-
mm/vmscan.c | 73 +++++++++++++++++++++++++++++++++-----------
7 files changed, 78 insertions(+), 32 deletions(-)
--
2.40.0.348.gf938b09366-goog
During reclaim, we keep track of pages reclaimed from other means than
LRU-based reclaim through scan_control->reclaim_state->reclaimed_slab,
which we stash a pointer to in current task_struct.
However, we keep track of more than just reclaimed slab pages through
this. We also use it for clean file pages dropped through pruned inodes,
and xfs buffer pages freed. Rename reclaimed_slab to reclaimed, and add
a helper function that wraps updating it through current, so that future
changes to this logic are contained within mm/vmscan.c.
Additionally, add a flush_reclaim_state() helper to wrap using
reclaim_state->reclaimed to updated sc->nr_reclaimed, and use that
helper to add an elaborate comment about why we only do the update for
global reclaim.
Finally, move set_task_reclaim_state() next to flush_reclaim_state() so
that all reclaim_state helpers are in close proximity for easier
readability.
Signed-off-by: Yosry Ahmed <[email protected]>
---
fs/inode.c | 3 +-
fs/xfs/xfs_buf.c | 3 +-
include/linux/swap.h | 17 +++++++++-
mm/slab.c | 3 +-
mm/slob.c | 6 ++--
mm/slub.c | 5 ++-
mm/vmscan.c | 75 ++++++++++++++++++++++++++++++++------------
7 files changed, 78 insertions(+), 34 deletions(-)
diff --git a/fs/inode.c b/fs/inode.c
index 4558dc2f13557..e60fcc41faf17 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -864,8 +864,7 @@ static enum lru_status inode_lru_isolate(struct list_head *item,
__count_vm_events(KSWAPD_INODESTEAL, reap);
else
__count_vm_events(PGINODESTEAL, reap);
- if (current->reclaim_state)
- current->reclaim_state->reclaimed_slab += reap;
+ mm_account_reclaimed_pages(reap);
}
iput(inode);
spin_lock(lru_lock);
diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index 54c774af6e1c6..15d1e5a7c2d34 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -286,8 +286,7 @@ xfs_buf_free_pages(
if (bp->b_pages[i])
__free_page(bp->b_pages[i]);
}
- if (current->reclaim_state)
- current->reclaim_state->reclaimed_slab += bp->b_page_count;
+ mm_account_reclaimed_pages(bp->b_page_count);
if (bp->b_pages != bp->b_page_array)
kmem_free(bp->b_pages);
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 209a425739a9f..e131ac155fb95 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -153,13 +153,28 @@ union swap_header {
* memory reclaim
*/
struct reclaim_state {
- unsigned long reclaimed_slab;
+ /* pages reclaimed outside of LRU-based reclaim */
+ unsigned long reclaimed;
#ifdef CONFIG_LRU_GEN
/* per-thread mm walk data */
struct lru_gen_mm_walk *mm_walk;
#endif
};
+/*
+ * mm_account_reclaimed_pages(): account reclaimed pages outside of LRU-based
+ * reclaim
+ * @pages: number of pages reclaimed
+ *
+ * If the current process is undergoing a reclaim operation, increment the
+ * number of reclaimed pages by @pages.
+ */
+static inline void mm_account_reclaimed_pages(unsigned long pages)
+{
+ if (current->reclaim_state)
+ current->reclaim_state->reclaimed += pages;
+}
+
#ifdef __KERNEL__
struct address_space;
diff --git a/mm/slab.c b/mm/slab.c
index dabc2a671fc6f..64bf1de817b24 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1392,8 +1392,7 @@ static void kmem_freepages(struct kmem_cache *cachep, struct slab *slab)
smp_wmb();
__folio_clear_slab(folio);
- if (current->reclaim_state)
- current->reclaim_state->reclaimed_slab += 1 << order;
+ mm_account_reclaimed_pages(1 << order);
unaccount_slab(slab, order, cachep);
__free_pages(&folio->page, order);
}
diff --git a/mm/slob.c b/mm/slob.c
index fe567fcfa3a39..79cc8680c973c 100644
--- a/mm/slob.c
+++ b/mm/slob.c
@@ -61,7 +61,7 @@
#include <linux/slab.h>
#include <linux/mm.h>
-#include <linux/swap.h> /* struct reclaim_state */
+#include <linux/swap.h> /* mm_account_reclaimed_pages() */
#include <linux/cache.h>
#include <linux/init.h>
#include <linux/export.h>
@@ -211,9 +211,7 @@ static void slob_free_pages(void *b, int order)
{
struct page *sp = virt_to_page(b);
- if (current->reclaim_state)
- current->reclaim_state->reclaimed_slab += 1 << order;
-
+ mm_account_reclaimed_pages(1 << order);
mod_node_page_state(page_pgdat(sp), NR_SLAB_UNRECLAIMABLE_B,
-(PAGE_SIZE << order));
__free_pages(sp, order);
diff --git a/mm/slub.c b/mm/slub.c
index 39327e98fce34..7aa30eef82350 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -11,7 +11,7 @@
*/
#include <linux/mm.h>
-#include <linux/swap.h> /* struct reclaim_state */
+#include <linux/swap.h> /* mm_account_reclaimed_pages() */
#include <linux/module.h>
#include <linux/bit_spinlock.h>
#include <linux/interrupt.h>
@@ -2063,8 +2063,7 @@ static void __free_slab(struct kmem_cache *s, struct slab *slab)
/* Make the mapping reset visible before clearing the flag */
smp_wmb();
__folio_clear_slab(folio);
- if (current->reclaim_state)
- current->reclaim_state->reclaimed_slab += pages;
+ mm_account_reclaimed_pages(pages);
unaccount_slab(slab, order, s);
__free_pages(&folio->page, order);
}
diff --git a/mm/vmscan.c b/mm/vmscan.c
index c82bd89f90364..049e39202e6ce 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -188,18 +188,6 @@ struct scan_control {
*/
int vm_swappiness = 60;
-static void set_task_reclaim_state(struct task_struct *task,
- struct reclaim_state *rs)
-{
- /* Check for an overwrite */
- WARN_ON_ONCE(rs && task->reclaim_state);
-
- /* Check for the nulling of an already-nulled member */
- WARN_ON_ONCE(!rs && !task->reclaim_state);
-
- task->reclaim_state = rs;
-}
-
LIST_HEAD(shrinker_list);
DECLARE_RWSEM(shrinker_rwsem);
@@ -511,6 +499,59 @@ static bool writeback_throttling_sane(struct scan_control *sc)
}
#endif
+static void set_task_reclaim_state(struct task_struct *task,
+ struct reclaim_state *rs)
+{
+ /* Check for an overwrite */
+ WARN_ON_ONCE(rs && task->reclaim_state);
+
+ /* Check for the nulling of an already-nulled member */
+ WARN_ON_ONCE(!rs && !task->reclaim_state);
+
+ task->reclaim_state = rs;
+}
+
+/*
+ * flush_reclaim_state(): add pages reclaimed outside of LRU-based reclaim to
+ * scan_control->nr_reclaimed.
+ */
+static void flush_reclaim_state(struct scan_control *sc,
+ struct reclaim_state *rs)
+{
+ /*
+ * Currently, reclaim_state->reclaimed includes three types of pages
+ * freed outside of vmscan:
+ * (1) Slab pages.
+ * (2) Clean file pages from pruned inodes.
+ * (3) XFS freed buffer pages.
+ *
+ * For all of these cases, we have no way of finding out whether these
+ * pages were related to the memcg under reclaim. For example, a freed
+ * slab page could have had only a single object charged to the memcg
+ * under reclaim. Also, populated inodes are not on shrinker LRUs
+ * anymore except on highmem systems.
+ *
+ * Instead of over-reporting the reclaimed pages in a memcg reclaim,
+ * only count such pages in global reclaim. This prevents unnecessary
+ * retries during memcg charging and false positive from proactive
+ * reclaim (memory.reclaim).
+ *
+ * For uncommon cases were the freed pages were actually significantly
+ * charged to the memcg under reclaim, and we end up under-reporting, it
+ * should be fine. The freed pages will be uncharged anyway, even if
+ * they are not reported properly, and we will be able to make forward
+ * progress in charging (which is usually in a retry loop).
+ *
+ * We can go one step further, and report the uncharged objcg pages in
+ * memcg reclaim, to make reporting more accurate and reduce
+ * under-reporting, but it's probably not worth the complexity for now.
+ */
+ if (rs && global_reclaim(sc)) {
+ sc->nr_reclaimed += rs->reclaimed;
+ rs->reclaimed = 0;
+ }
+}
+
static long xchg_nr_deferred(struct shrinker *shrinker,
struct shrink_control *sc)
{
@@ -5346,10 +5387,7 @@ static int shrink_one(struct lruvec *lruvec, struct scan_control *sc)
vmpressure(sc->gfp_mask, memcg, false, sc->nr_scanned - scanned,
sc->nr_reclaimed - reclaimed);
- if (global_reclaim(sc)) {
- sc->nr_reclaimed += current->reclaim_state->reclaimed_slab;
- current->reclaim_state->reclaimed_slab = 0;
- }
+ flush_reclaim_state(sc, current->reclaim_state);
return success ? MEMCG_LRU_YOUNG : 0;
}
@@ -6474,10 +6512,7 @@ static void shrink_node(pg_data_t *pgdat, struct scan_control *sc)
shrink_node_memcgs(pgdat, sc);
- if (reclaim_state && global_reclaim(sc)) {
- sc->nr_reclaimed += reclaim_state->reclaimed_slab;
- reclaim_state->reclaimed_slab = 0;
- }
+ flush_reclaim_state(sc, reclaim_state);
/* Record the subtree's reclaim efficiency */
if (!sc->proactive)
--
2.40.0.348.gf938b09366-goog
On Wed, 2023-04-05 at 18:54 +0000, Yosry Ahmed wrote:
> During reclaim, we keep track of pages reclaimed from other means than
> LRU-based reclaim through scan_control->reclaim_state->reclaimed_slab,
> which we stash a pointer to in current task_struct.
>
> However, we keep track of more than just reclaimed slab pages through
> this. We also use it for clean file pages dropped through pruned inodes,
> and xfs buffer pages freed. Rename reclaimed_slab to reclaimed, and add
> a helper function that wraps updating it through current, so that future
> changes to this logic are contained within mm/vmscan.c.
>
> Additionally, add a flush_reclaim_state() helper to wrap using
> reclaim_state->reclaimed to updated sc->nr_reclaimed, and use that
> helper to add an elaborate comment about why we only do the update for
> global reclaim.
>
> Finally, move set_task_reclaim_state() next to flush_reclaim_state() so
> that all reclaim_state helpers are in close proximity for easier
> readability.
>
> Signed-off-by: Yosry Ahmed <[email protected]>
> ---
> fs/inode.c | 3 +-
> fs/xfs/xfs_buf.c | 3 +-
> include/linux/swap.h | 17 +++++++++-
> mm/slab.c | 3 +-
> mm/slob.c | 6 ++--
> mm/slub.c | 5 ++-
> mm/vmscan.c | 75 ++++++++++++++++++++++++++++++++------------
> 7 files changed, 78 insertions(+), 34 deletions(-)
>
> diff --git a/fs/inode.c b/fs/inode.c
> index 4558dc2f13557..e60fcc41faf17 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -864,8 +864,7 @@ static enum lru_status inode_lru_isolate(struct list_head *item,
> __count_vm_events(KSWAPD_INODESTEAL, reap);
> else
> __count_vm_events(PGINODESTEAL, reap);
> - if (current->reclaim_state)
> - current->reclaim_state->reclaimed_slab += reap;
> + mm_account_reclaimed_pages(reap);
> }
> iput(inode);
> spin_lock(lru_lock);
> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> index 54c774af6e1c6..15d1e5a7c2d34 100644
> --- a/fs/xfs/xfs_buf.c
> +++ b/fs/xfs/xfs_buf.c
> @@ -286,8 +286,7 @@ xfs_buf_free_pages(
> if (bp->b_pages[i])
> __free_page(bp->b_pages[i]);
> }
> - if (current->reclaim_state)
> - current->reclaim_state->reclaimed_slab += bp->b_page_count;
> + mm_account_reclaimed_pages(bp->b_page_count);
>
> if (bp->b_pages != bp->b_page_array)
> kmem_free(bp->b_pages);
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 209a425739a9f..e131ac155fb95 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -153,13 +153,28 @@ union swap_header {
> * memory reclaim
> */
> struct reclaim_state {
> - unsigned long reclaimed_slab;
> + /* pages reclaimed outside of LRU-based reclaim */
> + unsigned long reclaimed;
> #ifdef CONFIG_LRU_GEN
> /* per-thread mm walk data */
> struct lru_gen_mm_walk *mm_walk;
> #endif
> };
>
> +/*
> + * mm_account_reclaimed_pages(): account reclaimed pages outside of LRU-based
> + * reclaim
> + * @pages: number of pages reclaimed
> + *
> + * If the current process is undergoing a reclaim operation, increment the
> + * number of reclaimed pages by @pages.
> + */
> +static inline void mm_account_reclaimed_pages(unsigned long pages)
> +{
> + if (current->reclaim_state)
> + current->reclaim_state->reclaimed += pages;
> +}
> +
> #ifdef __KERNEL__
>
> struct address_space;
> diff --git a/mm/slab.c b/mm/slab.c
> index dabc2a671fc6f..64bf1de817b24 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -1392,8 +1392,7 @@ static void kmem_freepages(struct kmem_cache *cachep, struct slab *slab)
> smp_wmb();
> __folio_clear_slab(folio);
>
> - if (current->reclaim_state)
> - current->reclaim_state->reclaimed_slab += 1 << order;
> + mm_account_reclaimed_pages(1 << order);
> unaccount_slab(slab, order, cachep);
> __free_pages(&folio->page, order);
> }
> diff --git a/mm/slob.c b/mm/slob.c
> index fe567fcfa3a39..79cc8680c973c 100644
> --- a/mm/slob.c
> +++ b/mm/slob.c
> @@ -61,7 +61,7 @@
> #include <linux/slab.h>
>
> #include <linux/mm.h>
> -#include <linux/swap.h> /* struct reclaim_state */
> +#include <linux/swap.h> /* mm_account_reclaimed_pages() */
> #include <linux/cache.h>
> #include <linux/init.h>
> #include <linux/export.h>
> @@ -211,9 +211,7 @@ static void slob_free_pages(void *b, int order)
> {
> struct page *sp = virt_to_page(b);
>
> - if (current->reclaim_state)
> - current->reclaim_state->reclaimed_slab += 1 << order;
> -
> + mm_account_reclaimed_pages(1 << order);
> mod_node_page_state(page_pgdat(sp), NR_SLAB_UNRECLAIMABLE_B,
> -(PAGE_SIZE << order));
> __free_pages(sp, order);
> diff --git a/mm/slub.c b/mm/slub.c
> index 39327e98fce34..7aa30eef82350 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -11,7 +11,7 @@
> */
>
> #include <linux/mm.h>
> -#include <linux/swap.h> /* struct reclaim_state */
> +#include <linux/swap.h> /* mm_account_reclaimed_pages() */
> #include <linux/module.h>
> #include <linux/bit_spinlock.h>
> #include <linux/interrupt.h>
> @@ -2063,8 +2063,7 @@ static void __free_slab(struct kmem_cache *s, struct slab *slab)
> /* Make the mapping reset visible before clearing the flag */
> smp_wmb();
> __folio_clear_slab(folio);
> - if (current->reclaim_state)
> - current->reclaim_state->reclaimed_slab += pages;
> + mm_account_reclaimed_pages(pages);
> unaccount_slab(slab, order, s);
> __free_pages(&folio->page, order);
> }
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index c82bd89f90364..049e39202e6ce 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -188,18 +188,6 @@ struct scan_control {
> */
> int vm_swappiness = 60;
>
> -static void set_task_reclaim_state(struct task_struct *task,
> - struct reclaim_state *rs)
> -{
> - /* Check for an overwrite */
> - WARN_ON_ONCE(rs && task->reclaim_state);
> -
> - /* Check for the nulling of an already-nulled member */
> - WARN_ON_ONCE(!rs && !task->reclaim_state);
> -
> - task->reclaim_state = rs;
> -}
> -
> LIST_HEAD(shrinker_list);
> DECLARE_RWSEM(shrinker_rwsem);
>
> @@ -511,6 +499,59 @@ static bool writeback_throttling_sane(struct scan_control *sc)
> }
> #endif
>
> +static void set_task_reclaim_state(struct task_struct *task,
> + struct reclaim_state *rs)
> +{
> + /* Check for an overwrite */
> + WARN_ON_ONCE(rs && task->reclaim_state);
> +
> + /* Check for the nulling of an already-nulled member */
> + WARN_ON_ONCE(!rs && !task->reclaim_state);
> +
> + task->reclaim_state = rs;
> +}
> +
> +/*
> + * flush_reclaim_state(): add pages reclaimed outside of LRU-based reclaim to
> + * scan_control->nr_reclaimed.
> + */
> +static void flush_reclaim_state(struct scan_control *sc,
> + struct reclaim_state *rs)
> +{
> + /*
> + * Currently, reclaim_state->reclaimed includes three types of pages
> + * freed outside of vmscan:
> + * (1) Slab pages.
> + * (2) Clean file pages from pruned inodes.
> + * (3) XFS freed buffer pages.
> + *
> + * For all of these cases, we have no way of finding out whether these
> + * pages were related to the memcg under reclaim. For example, a freed
> + * slab page could have had only a single object charged to the memcg
Minor nits:
s/could have had/could have
> + * under reclaim. Also, populated inodes are not on shrinker LRUs
> + * anymore except on highmem systems.
> + *
> + * Instead of over-reporting the reclaimed pages in a memcg reclaim,
> + * only count such pages in global reclaim. This prevents unnecessary
May be clearer to say:
This prevents under-reclaimaing the target memcg, and unnecessary
> + * retries during memcg charging and false positive from proactive
> + * reclaim (memory.reclaim).
> + *
Tim
On Thu, Apr 6, 2023 at 10:32 AM Tim Chen <[email protected]> wrote:
>
> On Wed, 2023-04-05 at 18:54 +0000, Yosry Ahmed wrote:
> > During reclaim, we keep track of pages reclaimed from other means than
> > LRU-based reclaim through scan_control->reclaim_state->reclaimed_slab,
> > which we stash a pointer to in current task_struct.
> >
> > However, we keep track of more than just reclaimed slab pages through
> > this. We also use it for clean file pages dropped through pruned inodes,
> > and xfs buffer pages freed. Rename reclaimed_slab to reclaimed, and add
> > a helper function that wraps updating it through current, so that future
> > changes to this logic are contained within mm/vmscan.c.
> >
> > Additionally, add a flush_reclaim_state() helper to wrap using
> > reclaim_state->reclaimed to updated sc->nr_reclaimed, and use that
> > helper to add an elaborate comment about why we only do the update for
> > global reclaim.
> >
> > Finally, move set_task_reclaim_state() next to flush_reclaim_state() so
> > that all reclaim_state helpers are in close proximity for easier
> > readability.
> >
> > Signed-off-by: Yosry Ahmed <[email protected]>
> > ---
> > fs/inode.c | 3 +-
> > fs/xfs/xfs_buf.c | 3 +-
> > include/linux/swap.h | 17 +++++++++-
> > mm/slab.c | 3 +-
> > mm/slob.c | 6 ++--
> > mm/slub.c | 5 ++-
> > mm/vmscan.c | 75 ++++++++++++++++++++++++++++++++------------
> > 7 files changed, 78 insertions(+), 34 deletions(-)
> >
> > diff --git a/fs/inode.c b/fs/inode.c
> > index 4558dc2f13557..e60fcc41faf17 100644
> > --- a/fs/inode.c
> > +++ b/fs/inode.c
> > @@ -864,8 +864,7 @@ static enum lru_status inode_lru_isolate(struct list_head *item,
> > __count_vm_events(KSWAPD_INODESTEAL, reap);
> > else
> > __count_vm_events(PGINODESTEAL, reap);
> > - if (current->reclaim_state)
> > - current->reclaim_state->reclaimed_slab += reap;
> > + mm_account_reclaimed_pages(reap);
> > }
> > iput(inode);
> > spin_lock(lru_lock);
> > diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> > index 54c774af6e1c6..15d1e5a7c2d34 100644
> > --- a/fs/xfs/xfs_buf.c
> > +++ b/fs/xfs/xfs_buf.c
> > @@ -286,8 +286,7 @@ xfs_buf_free_pages(
> > if (bp->b_pages[i])
> > __free_page(bp->b_pages[i]);
> > }
> > - if (current->reclaim_state)
> > - current->reclaim_state->reclaimed_slab += bp->b_page_count;
> > + mm_account_reclaimed_pages(bp->b_page_count);
> >
> > if (bp->b_pages != bp->b_page_array)
> > kmem_free(bp->b_pages);
> > diff --git a/include/linux/swap.h b/include/linux/swap.h
> > index 209a425739a9f..e131ac155fb95 100644
> > --- a/include/linux/swap.h
> > +++ b/include/linux/swap.h
> > @@ -153,13 +153,28 @@ union swap_header {
> > * memory reclaim
> > */
> > struct reclaim_state {
> > - unsigned long reclaimed_slab;
> > + /* pages reclaimed outside of LRU-based reclaim */
> > + unsigned long reclaimed;
> > #ifdef CONFIG_LRU_GEN
> > /* per-thread mm walk data */
> > struct lru_gen_mm_walk *mm_walk;
> > #endif
> > };
> >
> > +/*
> > + * mm_account_reclaimed_pages(): account reclaimed pages outside of LRU-based
> > + * reclaim
> > + * @pages: number of pages reclaimed
> > + *
> > + * If the current process is undergoing a reclaim operation, increment the
> > + * number of reclaimed pages by @pages.
> > + */
> > +static inline void mm_account_reclaimed_pages(unsigned long pages)
> > +{
> > + if (current->reclaim_state)
> > + current->reclaim_state->reclaimed += pages;
> > +}
> > +
> > #ifdef __KERNEL__
> >
> > struct address_space;
> > diff --git a/mm/slab.c b/mm/slab.c
> > index dabc2a671fc6f..64bf1de817b24 100644
> > --- a/mm/slab.c
> > +++ b/mm/slab.c
> > @@ -1392,8 +1392,7 @@ static void kmem_freepages(struct kmem_cache *cachep, struct slab *slab)
> > smp_wmb();
> > __folio_clear_slab(folio);
> >
> > - if (current->reclaim_state)
> > - current->reclaim_state->reclaimed_slab += 1 << order;
> > + mm_account_reclaimed_pages(1 << order);
> > unaccount_slab(slab, order, cachep);
> > __free_pages(&folio->page, order);
> > }
> > diff --git a/mm/slob.c b/mm/slob.c
> > index fe567fcfa3a39..79cc8680c973c 100644
> > --- a/mm/slob.c
> > +++ b/mm/slob.c
> > @@ -61,7 +61,7 @@
> > #include <linux/slab.h>
> >
> > #include <linux/mm.h>
> > -#include <linux/swap.h> /* struct reclaim_state */
> > +#include <linux/swap.h> /* mm_account_reclaimed_pages() */
> > #include <linux/cache.h>
> > #include <linux/init.h>
> > #include <linux/export.h>
> > @@ -211,9 +211,7 @@ static void slob_free_pages(void *b, int order)
> > {
> > struct page *sp = virt_to_page(b);
> >
> > - if (current->reclaim_state)
> > - current->reclaim_state->reclaimed_slab += 1 << order;
> > -
> > + mm_account_reclaimed_pages(1 << order);
> > mod_node_page_state(page_pgdat(sp), NR_SLAB_UNRECLAIMABLE_B,
> > -(PAGE_SIZE << order));
> > __free_pages(sp, order);
> > diff --git a/mm/slub.c b/mm/slub.c
> > index 39327e98fce34..7aa30eef82350 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -11,7 +11,7 @@
> > */
> >
> > #include <linux/mm.h>
> > -#include <linux/swap.h> /* struct reclaim_state */
> > +#include <linux/swap.h> /* mm_account_reclaimed_pages() */
> > #include <linux/module.h>
> > #include <linux/bit_spinlock.h>
> > #include <linux/interrupt.h>
> > @@ -2063,8 +2063,7 @@ static void __free_slab(struct kmem_cache *s, struct slab *slab)
> > /* Make the mapping reset visible before clearing the flag */
> > smp_wmb();
> > __folio_clear_slab(folio);
> > - if (current->reclaim_state)
> > - current->reclaim_state->reclaimed_slab += pages;
> > + mm_account_reclaimed_pages(pages);
> > unaccount_slab(slab, order, s);
> > __free_pages(&folio->page, order);
> > }
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index c82bd89f90364..049e39202e6ce 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -188,18 +188,6 @@ struct scan_control {
> > */
> > int vm_swappiness = 60;
> >
> > -static void set_task_reclaim_state(struct task_struct *task,
> > - struct reclaim_state *rs)
> > -{
> > - /* Check for an overwrite */
> > - WARN_ON_ONCE(rs && task->reclaim_state);
> > -
> > - /* Check for the nulling of an already-nulled member */
> > - WARN_ON_ONCE(!rs && !task->reclaim_state);
> > -
> > - task->reclaim_state = rs;
> > -}
> > -
> > LIST_HEAD(shrinker_list);
> > DECLARE_RWSEM(shrinker_rwsem);
> >
> > @@ -511,6 +499,59 @@ static bool writeback_throttling_sane(struct scan_control *sc)
> > }
> > #endif
> >
> > +static void set_task_reclaim_state(struct task_struct *task,
> > + struct reclaim_state *rs)
> > +{
> > + /* Check for an overwrite */
> > + WARN_ON_ONCE(rs && task->reclaim_state);
> > +
> > + /* Check for the nulling of an already-nulled member */
> > + WARN_ON_ONCE(!rs && !task->reclaim_state);
> > +
> > + task->reclaim_state = rs;
> > +}
> > +
> > +/*
> > + * flush_reclaim_state(): add pages reclaimed outside of LRU-based reclaim to
> > + * scan_control->nr_reclaimed.
> > + */
> > +static void flush_reclaim_state(struct scan_control *sc,
> > + struct reclaim_state *rs)
> > +{
> > + /*
> > + * Currently, reclaim_state->reclaimed includes three types of pages
> > + * freed outside of vmscan:
> > + * (1) Slab pages.
> > + * (2) Clean file pages from pruned inodes.
> > + * (3) XFS freed buffer pages.
> > + *
> > + * For all of these cases, we have no way of finding out whether these
> > + * pages were related to the memcg under reclaim. For example, a freed
> > + * slab page could have had only a single object charged to the memcg
>
> Minor nits:
> s/could have had/could have
>
> > + * under reclaim. Also, populated inodes are not on shrinker LRUs
> > + * anymore except on highmem systems.
> > + *
> > + * Instead of over-reporting the reclaimed pages in a memcg reclaim,
> > + * only count such pages in global reclaim. This prevents unnecessary
>
> May be clearer to say:
> This prevents under-reclaimaing the target memcg, and unnecessary
Thanks, will rephrase for the next version!
>
> > + * retries during memcg charging and false positive from proactive
> > + * reclaim (memory.reclaim).
> > + *
>
> Tim
>
On Thu, Apr 06, 2023 at 10:31:53AM -0700, Tim Chen wrote:
> On Wed, 2023-04-05 at 18:54 +0000, Yosry Ahmed wrote:
> > + * For all of these cases, we have no way of finding out whether these
> > + * pages were related to the memcg under reclaim. For example, a freed
> > + * slab page could have had only a single object charged to the memcg
>
> Minor nits:
> s/could have had/could have
No ... "could have had" is correct. I'm a native English speaker, so I
have no idea what the rule here is, but I can ask my linguist wife later
if you want to know ;-)
Maybe it's something like this:
https://www.englishgrammar.org/have-had-and-had-had/
Hi, Yosry,
On Wed, Apr 05, 2023 at 06:54:27PM +0000, Yosry Ahmed wrote:
[...]
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index c82bd89f90364..049e39202e6ce 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -188,18 +188,6 @@ struct scan_control {
> */
> int vm_swappiness = 60;
>
> -static void set_task_reclaim_state(struct task_struct *task,
> - struct reclaim_state *rs)
> -{
> - /* Check for an overwrite */
> - WARN_ON_ONCE(rs && task->reclaim_state);
> -
> - /* Check for the nulling of an already-nulled member */
> - WARN_ON_ONCE(!rs && !task->reclaim_state);
> -
> - task->reclaim_state = rs;
> -}
> -
> LIST_HEAD(shrinker_list);
> DECLARE_RWSEM(shrinker_rwsem);
>
> @@ -511,6 +499,59 @@ static bool writeback_throttling_sane(struct scan_control *sc)
> }
> #endif
>
> +static void set_task_reclaim_state(struct task_struct *task,
> + struct reclaim_state *rs)
> +{
> + /* Check for an overwrite */
> + WARN_ON_ONCE(rs && task->reclaim_state);
> +
> + /* Check for the nulling of an already-nulled member */
> + WARN_ON_ONCE(!rs && !task->reclaim_state);
> +
> + task->reclaim_state = rs;
> +}
Nit: I just think such movement not necessary while it loses the "git
blame" information easily.
Instead of moving this here without major benefit, why not just define
flush_reclaim_state() right after previous set_task_reclaim_state()?
> +
> +/*
> + * flush_reclaim_state(): add pages reclaimed outside of LRU-based reclaim to
> + * scan_control->nr_reclaimed.
> + */
> +static void flush_reclaim_state(struct scan_control *sc,
> + struct reclaim_state *rs)
> +{
> + /*
> + * Currently, reclaim_state->reclaimed includes three types of pages
> + * freed outside of vmscan:
> + * (1) Slab pages.
> + * (2) Clean file pages from pruned inodes.
> + * (3) XFS freed buffer pages.
> + *
> + * For all of these cases, we have no way of finding out whether these
> + * pages were related to the memcg under reclaim. For example, a freed
> + * slab page could have had only a single object charged to the memcg
> + * under reclaim. Also, populated inodes are not on shrinker LRUs
> + * anymore except on highmem systems.
> + *
> + * Instead of over-reporting the reclaimed pages in a memcg reclaim,
> + * only count such pages in global reclaim. This prevents unnecessary
> + * retries during memcg charging and false positive from proactive
> + * reclaim (memory.reclaim).
> + *
> + * For uncommon cases were the freed pages were actually significantly
> + * charged to the memcg under reclaim, and we end up under-reporting, it
> + * should be fine. The freed pages will be uncharged anyway, even if
> + * they are not reported properly, and we will be able to make forward
> + * progress in charging (which is usually in a retry loop).
> + *
> + * We can go one step further, and report the uncharged objcg pages in
> + * memcg reclaim, to make reporting more accurate and reduce
> + * under-reporting, but it's probably not worth the complexity for now.
> + */
> + if (rs && global_reclaim(sc)) {
> + sc->nr_reclaimed += rs->reclaimed;
> + rs->reclaimed = 0;
> + }
> +}
> +
> static long xchg_nr_deferred(struct shrinker *shrinker,
> struct shrink_control *sc)
> {
> @@ -5346,10 +5387,7 @@ static int shrink_one(struct lruvec *lruvec, struct scan_control *sc)
> vmpressure(sc->gfp_mask, memcg, false, sc->nr_scanned - scanned,
> sc->nr_reclaimed - reclaimed);
>
> - if (global_reclaim(sc)) {
> - sc->nr_reclaimed += current->reclaim_state->reclaimed_slab;
> - current->reclaim_state->reclaimed_slab = 0;
> - }
> + flush_reclaim_state(sc, current->reclaim_state);
>
> return success ? MEMCG_LRU_YOUNG : 0;
> }
> @@ -6474,10 +6512,7 @@ static void shrink_node(pg_data_t *pgdat, struct scan_control *sc)
>
> shrink_node_memcgs(pgdat, sc);
>
> - if (reclaim_state && global_reclaim(sc)) {
> - sc->nr_reclaimed += reclaim_state->reclaimed_slab;
> - reclaim_state->reclaimed_slab = 0;
> - }
> + flush_reclaim_state(sc, reclaim_state);
IIUC reclaim_state here still points to current->reclaim_state. Could it
change at all?
Is it cleaner to make flush_reclaim_state() taking "sc" only if it always
references current->reclaim_state?
>
> /* Record the subtree's reclaim efficiency */
> if (!sc->proactive)
> --
> 2.40.0.348.gf938b09366-goog
>
--
Peter Xu
On Thu, Apr 6, 2023 at 1:45 PM Peter Xu <[email protected]> wrote:
>
> Hi, Yosry,
>
> On Wed, Apr 05, 2023 at 06:54:27PM +0000, Yosry Ahmed wrote:
>
> [...]
>
> > diff --git a/mm/vmscan.c b/mm/vmscan.c
> > index c82bd89f90364..049e39202e6ce 100644
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -188,18 +188,6 @@ struct scan_control {
> > */
> > int vm_swappiness = 60;
> >
> > -static void set_task_reclaim_state(struct task_struct *task,
> > - struct reclaim_state *rs)
> > -{
> > - /* Check for an overwrite */
> > - WARN_ON_ONCE(rs && task->reclaim_state);
> > -
> > - /* Check for the nulling of an already-nulled member */
> > - WARN_ON_ONCE(!rs && !task->reclaim_state);
> > -
> > - task->reclaim_state = rs;
> > -}
> > -
> > LIST_HEAD(shrinker_list);
> > DECLARE_RWSEM(shrinker_rwsem);
> >
> > @@ -511,6 +499,59 @@ static bool writeback_throttling_sane(struct scan_control *sc)
> > }
> > #endif
> >
> > +static void set_task_reclaim_state(struct task_struct *task,
> > + struct reclaim_state *rs)
> > +{
> > + /* Check for an overwrite */
> > + WARN_ON_ONCE(rs && task->reclaim_state);
> > +
> > + /* Check for the nulling of an already-nulled member */
> > + WARN_ON_ONCE(!rs && !task->reclaim_state);
> > +
> > + task->reclaim_state = rs;
> > +}
>
> Nit: I just think such movement not necessary while it loses the "git
> blame" information easily.
>
> Instead of moving this here without major benefit, why not just define
> flush_reclaim_state() right after previous set_task_reclaim_state()?
An earlier version did that, but we would have to add a forward
declaration of global_reclaim() (or cgroup_reclaim()), as they are
defined after the previous position of set_task_reclaim_state().
>
> > +
> > +/*
> > + * flush_reclaim_state(): add pages reclaimed outside of LRU-based reclaim to
> > + * scan_control->nr_reclaimed.
> > + */
> > +static void flush_reclaim_state(struct scan_control *sc,
> > + struct reclaim_state *rs)
> > +{
> > + /*
> > + * Currently, reclaim_state->reclaimed includes three types of pages
> > + * freed outside of vmscan:
> > + * (1) Slab pages.
> > + * (2) Clean file pages from pruned inodes.
> > + * (3) XFS freed buffer pages.
> > + *
> > + * For all of these cases, we have no way of finding out whether these
> > + * pages were related to the memcg under reclaim. For example, a freed
> > + * slab page could have had only a single object charged to the memcg
> > + * under reclaim. Also, populated inodes are not on shrinker LRUs
> > + * anymore except on highmem systems.
> > + *
> > + * Instead of over-reporting the reclaimed pages in a memcg reclaim,
> > + * only count such pages in global reclaim. This prevents unnecessary
> > + * retries during memcg charging and false positive from proactive
> > + * reclaim (memory.reclaim).
> > + *
> > + * For uncommon cases were the freed pages were actually significantly
> > + * charged to the memcg under reclaim, and we end up under-reporting, it
> > + * should be fine. The freed pages will be uncharged anyway, even if
> > + * they are not reported properly, and we will be able to make forward
> > + * progress in charging (which is usually in a retry loop).
> > + *
> > + * We can go one step further, and report the uncharged objcg pages in
> > + * memcg reclaim, to make reporting more accurate and reduce
> > + * under-reporting, but it's probably not worth the complexity for now.
> > + */
> > + if (rs && global_reclaim(sc)) {
> > + sc->nr_reclaimed += rs->reclaimed;
> > + rs->reclaimed = 0;
> > + }
> > +}
> > +
> > static long xchg_nr_deferred(struct shrinker *shrinker,
> > struct shrink_control *sc)
> > {
> > @@ -5346,10 +5387,7 @@ static int shrink_one(struct lruvec *lruvec, struct scan_control *sc)
> > vmpressure(sc->gfp_mask, memcg, false, sc->nr_scanned - scanned,
> > sc->nr_reclaimed - reclaimed);
> >
> > - if (global_reclaim(sc)) {
> > - sc->nr_reclaimed += current->reclaim_state->reclaimed_slab;
> > - current->reclaim_state->reclaimed_slab = 0;
> > - }
> > + flush_reclaim_state(sc, current->reclaim_state);
> >
> > return success ? MEMCG_LRU_YOUNG : 0;
> > }
> > @@ -6474,10 +6512,7 @@ static void shrink_node(pg_data_t *pgdat, struct scan_control *sc)
> >
> > shrink_node_memcgs(pgdat, sc);
> >
> > - if (reclaim_state && global_reclaim(sc)) {
> > - sc->nr_reclaimed += reclaim_state->reclaimed_slab;
> > - reclaim_state->reclaimed_slab = 0;
> > - }
> > + flush_reclaim_state(sc, reclaim_state);
>
> IIUC reclaim_state here still points to current->reclaim_state. Could it
> change at all?
>
> Is it cleaner to make flush_reclaim_state() taking "sc" only if it always
> references current->reclaim_state?
Good point. I think it's always current->reclaim_state.
I think we can make flush_reclaim_state() only take "sc" as an
argument, and remove the "reclaim_state" local variable in
shrink_node() completely.
>
> >
> > /* Record the subtree's reclaim efficiency */
> > if (!sc->proactive)
> > --
> > 2.40.0.348.gf938b09366-goog
> >
>
> --
> Peter Xu
>