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SubjectRe: [PATCH 31/31] mm, vmstat: Remove zone and node double accounting by approximating retries
On Fri, Jul 01, 2016 at 09:01:39PM +0100, Mel Gorman wrote:
> The number of LRU pages, dirty pages and writeback pages must be accounted
> for on both zones and nodes because of the reclaim retry logic, compaction
> retry logic and highmem calculations all depending on per-zone stats.
>
> The retry logic is only critical for allocations that can use any zones.

Sorry, I cannot follow this assertion.
Could you explain?

> Hence this patch will not retry reclaim or compaction for such allocations.

What is such allocations?

> This should not be a problem for reclaim as zone-constrained allocations
> are immune from OOM kill. For retries, a very rough approximation is made

zone-constrained allocations are immune from OOM kill?
Please explain it, too.

Sorry for the many questions but I cannot review code without clear
understanding of assumption/background which I couldn't notice.

> whether to retry or not. While it is possible this will make the wrong
> decision on occasion, it will not infinite loop as the number of reclaim
> attempts is capped by MAX_RECLAIM_RETRIES.
>
> The highmem calculations only care about the global count of file pages
> in highmem. Hence, a global counter is used instead of per-zone stats.
> With this, the per-zone double accounting disappears.
>
> Suggested by: Michal Hocko <mhocko@kernel.org>
> Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
> ---
> include/linux/mm_inline.h | 20 +++++++++++--
> include/linux/mmzone.h | 4 ---
> include/linux/swap.h | 1 -
> mm/compaction.c | 22 ++++++++++++++-
> mm/migrate.c | 2 --
> mm/page-writeback.c | 13 ++++-----
> mm/page_alloc.c | 71 ++++++++++++++++++++++++++++++++---------------
> mm/vmscan.c | 16 -----------
> mm/vmstat.c | 3 --
> 9 files changed, 92 insertions(+), 60 deletions(-)
>
> diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
> index 9aadcc781857..c68680aac044 100644
> --- a/include/linux/mm_inline.h
> +++ b/include/linux/mm_inline.h
> @@ -4,6 +4,22 @@
> #include <linux/huge_mm.h>
> #include <linux/swap.h>
>
> +#ifdef CONFIG_HIGHMEM
> +extern unsigned long highmem_file_pages;
> +
> +static inline void acct_highmem_file_pages(int zid, enum lru_list lru,
> + int nr_pages)
> +{
> + if (is_highmem_idx(zid) && is_file_lru(lru))
> + highmem_file_pages += nr_pages;
> +}
> +#else
> +static inline void acct_highmem_file_pages(int zid, enum lru_list lru,
> + int nr_pages)
> +{
> +}
> +#endif
> +
> /**
> * page_is_file_cache - should the page be on a file LRU or anon LRU?
> * @page: the page to test
> @@ -29,9 +45,7 @@ static __always_inline void __update_lru_size(struct lruvec *lruvec,
> struct pglist_data *pgdat = lruvec_pgdat(lruvec);
>
> __mod_node_page_state(pgdat, NR_LRU_BASE + lru, nr_pages);
> - __mod_zone_page_state(&pgdat->node_zones[zid],
> - NR_ZONE_LRU_BASE + !!is_file_lru(lru),
> - nr_pages);
> + acct_highmem_file_pages(zid, lru, nr_pages);
> }
>
> static __always_inline void update_lru_size(struct lruvec *lruvec,
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index facee6b83440..9268528c20c0 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -110,10 +110,6 @@ struct zone_padding {
> enum zone_stat_item {
> /* First 128 byte cacheline (assuming 64 bit words) */
> NR_FREE_PAGES,
> - NR_ZONE_LRU_BASE, /* Used only for compaction and reclaim retry */
> - NR_ZONE_LRU_ANON = NR_ZONE_LRU_BASE,
> - NR_ZONE_LRU_FILE,
> - NR_ZONE_WRITE_PENDING, /* Count of dirty, writeback and unstable pages */
> NR_MLOCK, /* mlock()ed pages found and moved off LRU */
> NR_SLAB_RECLAIMABLE,
> NR_SLAB_UNRECLAIMABLE,
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index b17cc4830fa6..cc753c639e3d 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -307,7 +307,6 @@ extern void lru_cache_add_active_or_unevictable(struct page *page,
> struct vm_area_struct *vma);
>
> /* linux/mm/vmscan.c */
> -extern unsigned long zone_reclaimable_pages(struct zone *zone);
> extern unsigned long pgdat_reclaimable_pages(struct pglist_data *pgdat);
> extern unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
> gfp_t gfp_mask, nodemask_t *mask);
> diff --git a/mm/compaction.c b/mm/compaction.c
> index a0bd85712516..dfe7dafe8e8b 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -1446,6 +1446,13 @@ bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
> {
> struct zone *zone;
> struct zoneref *z;
> + pg_data_t *last_pgdat = NULL;
> +
> +#ifdef CONFIG_HIGHMEM
> + /* Do not retry compaction for zone-constrained allocations */
> + if (!is_highmem_idx(ac->high_zoneidx))
> + return false;
> +#endif
>
> /*
> * Make sure at least one zone would pass __compaction_suitable if we continue
> @@ -1456,14 +1463,27 @@ bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
> unsigned long available;
> enum compact_result compact_result;
>
> + if (last_pgdat == zone->zone_pgdat)
> + continue;
> +
> + /*
> + * This over-estimates the number of pages available for
> + * reclaim/compaction but walking the LRU would take too
> + * long. The consequences are that compaction may retry
> + * longer than it should for a zone-constrained allocation
> + * request.
> + */
> + last_pgdat = zone->zone_pgdat;
> + available = pgdat_reclaimable_pages(zone->zone_pgdat) / order;
> +
> /*
> * Do not consider all the reclaimable memory because we do not
> * want to trash just for a single high order allocation which
> * is even not guaranteed to appear even if __compaction_suitable
> * is happy about the watermark check.
> */
> - available = zone_reclaimable_pages(zone) / order;
> available += zone_page_state_snapshot(zone, NR_FREE_PAGES);
> + available = min(zone->managed_pages, available);
> compact_result = __compaction_suitable(zone, order, alloc_flags,
> ac_classzone_idx(ac), available);
> if (compact_result != COMPACT_SKIPPED &&
> diff --git a/mm/migrate.c b/mm/migrate.c
> index c77997dc6ed7..ed2f85e61de1 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -513,9 +513,7 @@ int migrate_page_move_mapping(struct address_space *mapping,
> }
> if (dirty && mapping_cap_account_dirty(mapping)) {
> __dec_node_state(oldzone->zone_pgdat, NR_FILE_DIRTY);
> - __dec_zone_state(oldzone, NR_ZONE_WRITE_PENDING);
> __inc_node_state(newzone->zone_pgdat, NR_FILE_DIRTY);
> - __dec_zone_state(newzone, NR_ZONE_WRITE_PENDING);
> }
> }
> local_irq_enable();
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 3c02aa603f5a..8db1db234915 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -299,6 +299,9 @@ static unsigned long node_dirtyable_memory(struct pglist_data *pgdat)
>
> return nr_pages;
> }
> +#ifdef CONFIG_HIGHMEM
> +unsigned long highmem_file_pages;
> +#endif
>
> static unsigned long highmem_dirtyable_memory(unsigned long total)
> {
> @@ -306,18 +309,17 @@ static unsigned long highmem_dirtyable_memory(unsigned long total)
> int node;
> unsigned long x = 0;
> int i;
> + unsigned long dirtyable = highmem_file_pages;
>
> for_each_node_state(node, N_HIGH_MEMORY) {
> for (i = ZONE_NORMAL + 1; i < MAX_NR_ZONES; i++) {
> struct zone *z;
> - unsigned long dirtyable;
>
> if (!is_highmem_idx(i))
> continue;
>
> z = &NODE_DATA(node)->node_zones[i];
> - dirtyable = zone_page_state(z, NR_FREE_PAGES) +
> - zone_page_state(z, NR_ZONE_LRU_FILE);
> + dirtyable += zone_page_state(z, NR_FREE_PAGES);
>
> /* watch for underflows */
> dirtyable -= min(dirtyable, high_wmark_pages(z));
> @@ -2460,7 +2462,6 @@ void account_page_dirtied(struct page *page, struct address_space *mapping)
>
> mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_DIRTY);
> __inc_node_page_state(page, NR_FILE_DIRTY);
> - __inc_zone_page_state(page, NR_ZONE_WRITE_PENDING);
> __inc_node_page_state(page, NR_DIRTIED);
> __inc_wb_stat(wb, WB_RECLAIMABLE);
> __inc_wb_stat(wb, WB_DIRTIED);
> @@ -2482,7 +2483,6 @@ void account_page_cleaned(struct page *page, struct address_space *mapping,
> if (mapping_cap_account_dirty(mapping)) {
> mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_DIRTY);
> dec_node_page_state(page, NR_FILE_DIRTY);
> - dec_zone_page_state(page, NR_ZONE_WRITE_PENDING);
> dec_wb_stat(wb, WB_RECLAIMABLE);
> task_io_account_cancelled_write(PAGE_SIZE);
> }
> @@ -2739,7 +2739,6 @@ int clear_page_dirty_for_io(struct page *page)
> if (TestClearPageDirty(page)) {
> mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_DIRTY);
> dec_node_page_state(page, NR_FILE_DIRTY);
> - dec_zone_page_state(page, NR_ZONE_WRITE_PENDING);
> dec_wb_stat(wb, WB_RECLAIMABLE);
> ret = 1;
> }
> @@ -2786,7 +2785,6 @@ int test_clear_page_writeback(struct page *page)
> if (ret) {
> mem_cgroup_dec_page_stat(page, MEM_CGROUP_STAT_WRITEBACK);
> dec_node_page_state(page, NR_WRITEBACK);
> - dec_zone_page_state(page, NR_ZONE_WRITE_PENDING);
> inc_node_page_state(page, NR_WRITTEN);
> }
> unlock_page_memcg(page);
> @@ -2841,7 +2839,6 @@ int __test_set_page_writeback(struct page *page, bool keep_write)
> if (!ret) {
> mem_cgroup_inc_page_stat(page, MEM_CGROUP_STAT_WRITEBACK);
> inc_node_page_state(page, NR_WRITEBACK);
> - inc_zone_page_state(page, NR_ZONE_WRITE_PENDING);
> }
> unlock_page_memcg(page);
> return ret;
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index d3eb15c35bb1..9581185cb31a 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3445,6 +3445,7 @@ should_reclaim_retry(gfp_t gfp_mask, unsigned order,
> {
> struct zone *zone;
> struct zoneref *z;
> + pg_data_t *current_pgdat = NULL;
>
> /*
> * Make sure we converge to OOM if we cannot make any progress
> @@ -3454,6 +3455,14 @@ should_reclaim_retry(gfp_t gfp_mask, unsigned order,
> return false;
>
> /*
> + * Blindly retry allocation requests that cannot use all zones. We do
> + * not have a reliable and fast means of calculating reclaimable, dirty
> + * and writeback pages in eligible zones.
> + */
> + if (IS_ENABLED(CONFIG_HIGHMEM) && !is_highmem_idx(gfp_zone(gfp_mask)))
> + goto out;
> +
> + /*
> * Keep reclaiming pages while there is a chance this will lead somewhere.
> * If none of the target zones can satisfy our allocation request even
> * if all reclaimable pages are considered then we are screwed and have
> @@ -3463,36 +3472,54 @@ should_reclaim_retry(gfp_t gfp_mask, unsigned order,
> ac->nodemask) {
> unsigned long available;
> unsigned long reclaimable;
> + unsigned long write_pending = 0;
> + int zid;
> +
> + if (current_pgdat == zone->zone_pgdat)
> + continue;
>
> - available = reclaimable = zone_reclaimable_pages(zone);
> + current_pgdat = zone->zone_pgdat;
> + available = reclaimable = pgdat_reclaimable_pages(current_pgdat);
> available -= DIV_ROUND_UP(no_progress_loops * available,
> MAX_RECLAIM_RETRIES);
> - available += zone_page_state_snapshot(zone, NR_FREE_PAGES);
> + write_pending = node_page_state(current_pgdat, NR_WRITEBACK) +
> + node_page_state(current_pgdat, NR_FILE_DIRTY);
>
> - /*
> - * Would the allocation succeed if we reclaimed the whole
> - * available?
> - */
> - if (__zone_watermark_ok(zone, order, min_wmark_pages(zone),
> - ac_classzone_idx(ac), alloc_flags, available)) {
> - /*
> - * If we didn't make any progress and have a lot of
> - * dirty + writeback pages then we should wait for
> - * an IO to complete to slow down the reclaim and
> - * prevent from pre mature OOM
> - */
> - if (!did_some_progress) {
> - unsigned long write_pending;
> + /* Account for all free pages on eligible zones */
> + for (zid = 0; zid <= zone_idx(zone); zid++) {
> + struct zone *acct_zone = &current_pgdat->node_zones[zid];
>
> - write_pending = zone_page_state_snapshot(zone,
> - NR_ZONE_WRITE_PENDING);
> + available += zone_page_state_snapshot(acct_zone, NR_FREE_PAGES);
> + }
>
> - if (2 * write_pending > reclaimable) {
> - congestion_wait(BLK_RW_ASYNC, HZ/10);
> - return true;
> - }
> + /*
> + * If we didn't make any progress and have a lot of
> + * dirty + writeback pages then we should wait for an IO to
> + * complete to slow down the reclaim and prevent from premature
> + * OOM.
> + */
> + if (!did_some_progress) {
> + if (2 * write_pending > reclaimable) {
> + congestion_wait(BLK_RW_ASYNC, HZ/10);
> + return true;
> }
> + }
>
> + /*
> + * Would the allocation succeed if we reclaimed the whole
> + * available? This is approximate because there is no
> + * accurate count of reclaimable pages per zone.
> + */
> + for (zid = 0; zid <= zone_idx(zone); zid++) {
> + struct zone *check_zone = &current_pgdat->node_zones[zid];
> + unsigned long estimate;
> +
> + estimate = min(check_zone->managed_pages, available);
> + if (__zone_watermark_ok(check_zone, order,
> + min_wmark_pages(check_zone), ac_classzone_idx(ac),
> + alloc_flags, available)) {
> + }
> +out:
> /*
> * Memory allocation/reclaim might be called from a WQ
> * context and the current implementation of the WQ
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 151c30dd27e2..c538a8cab43b 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -194,22 +194,6 @@ static bool sane_reclaim(struct scan_control *sc)
> }
> #endif
>
> -/*
> - * This misses isolated pages which are not accounted for to save counters.
> - * As the data only determines if reclaim or compaction continues, it is
> - * not expected that isolated pages will be a dominating factor.
> - */
> -unsigned long zone_reclaimable_pages(struct zone *zone)
> -{
> - unsigned long nr;
> -
> - nr = zone_page_state_snapshot(zone, NR_ZONE_LRU_FILE);
> - if (get_nr_swap_pages() > 0)
> - nr += zone_page_state_snapshot(zone, NR_ZONE_LRU_ANON);
> -
> - return nr;
> -}
> -
> unsigned long pgdat_reclaimable_pages(struct pglist_data *pgdat)
> {
> unsigned long nr;
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index ce09be63e8c7..524c082072be 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -908,9 +908,6 @@ int fragmentation_index(struct zone *zone, unsigned int order)
> const char * const vmstat_text[] = {
> /* enum zone_stat_item countes */
> "nr_free_pages",
> - "nr_zone_anon_lru",
> - "nr_zone_file_lru",
> - "nr_zone_write_pending",
> "nr_mlock",
> "nr_slab_reclaimable",
> "nr_slab_unreclaimable",
> --
> 2.6.4
>
> --
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