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 <yosryahmed@xxxxxxxxxx>
> ---
> 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
