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SubjectRe: [PATCH] mm: compaction: Partially revert capture of suitable high-order page
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On Fri, 2013-01-11 at 09:27 +0000, Mel Gorman wrote:
> Eric Wong reported on 3.7 and 3.8-rc2 that ppoll() got stuck when waiting
> for POLLIN on a local TCP socket. It was easier to trigger if there was disk
> IO and dirty pages at the same time and he bisected it to commit 1fb3f8ca
> "mm: compaction: capture a suitable high-order page immediately when it
> is made available".
>
> The intention of that patch was to improve high-order allocations under
> memory pressure after changes made to reclaim in 3.6 drastically hurt
> THP allocations but the approach was flawed. For Eric, the problem was
> that page->pfmemalloc was not being cleared for captured pages leading to
> a poor interaction with swap-over-NFS support causing the packets to be
> dropped. However, I identified a few more problems with the patch including
> the fact that it can increase contention on zone->lock in some cases which
> could result in async direct compaction being aborted early.
>
> In retrospect the capture patch took the wrong approach. What it should
> have done is mark the pageblock being migrated as MIGRATE_ISOLATE if it
> was allocating for THP and avoided races that way. While the patch was

Hi Mel,

Mark pageblock being migrated as MIGRATE_ISOLATE if it was allocating
for THP and avoided races that way is a good idea. But why I can't see
you do it in this patch?

> showing to improve allocation success rates at the time, the benefit is
> marginal given the relative complexity and it should be revisited from
> scratch in the context of the other reclaim-related changes that have taken
> place since the patch was first written and tested. This patch partially
> reverts commit 1fb3f8ca "mm: compaction: capture a suitable high-order
> page immediately when it is made available".
>
> Reported-and-tested-by: Eric Wong <normalperson@yhbt.net>
> Tested-by: Eric Dumazet <eric.dumazet@gmail.com>
> Cc: stable@vger.kernel.org
> Signed-off-by: Mel Gorman <mgorman@suse.de>
> ---
> include/linux/compaction.h | 4 +-
> include/linux/mm.h | 1 -
> mm/compaction.c | 92 +++++++-------------------------------------
> mm/internal.h | 1 -
> mm/page_alloc.c | 35 ++++-------------
> 5 files changed, 23 insertions(+), 110 deletions(-)
>
> diff --git a/include/linux/compaction.h b/include/linux/compaction.h
> index 6ecb6dc..cc7bdde 100644
> --- a/include/linux/compaction.h
> +++ b/include/linux/compaction.h
> @@ -22,7 +22,7 @@ extern int sysctl_extfrag_handler(struct ctl_table *table, int write,
> extern int fragmentation_index(struct zone *zone, unsigned int order);
> extern unsigned long try_to_compact_pages(struct zonelist *zonelist,
> int order, gfp_t gfp_mask, nodemask_t *mask,
> - bool sync, bool *contended, struct page **page);
> + bool sync, bool *contended);
> extern int compact_pgdat(pg_data_t *pgdat, int order);
> extern void reset_isolation_suitable(pg_data_t *pgdat);
> extern unsigned long compaction_suitable(struct zone *zone, int order);
> @@ -75,7 +75,7 @@ static inline bool compaction_restarting(struct zone *zone, int order)
> #else
> static inline unsigned long try_to_compact_pages(struct zonelist *zonelist,
> int order, gfp_t gfp_mask, nodemask_t *nodemask,
> - bool sync, bool *contended, struct page **page)
> + bool sync, bool *contended)
> {
> return COMPACT_CONTINUE;
> }
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 6320407..66e2f7c 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -455,7 +455,6 @@ void put_pages_list(struct list_head *pages);
>
> void split_page(struct page *page, unsigned int order);
> int split_free_page(struct page *page);
> -int capture_free_page(struct page *page, int alloc_order, int migratetype);
>
> /*
> * Compound pages have a destructor function. Provide a
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 6b807e4..2c57043 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -816,6 +816,7 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
> static int compact_finished(struct zone *zone,
> struct compact_control *cc)
> {
> + unsigned int order;
> unsigned long watermark;
>
> if (fatal_signal_pending(current))
> @@ -850,22 +851,16 @@ static int compact_finished(struct zone *zone,
> return COMPACT_CONTINUE;
>
> /* Direct compactor: Is a suitable page free? */
> - if (cc->page) {
> - /* Was a suitable page captured? */
> - if (*cc->page)
> + for (order = cc->order; order < MAX_ORDER; order++) {
> + struct free_area *area = &zone->free_area[order];
> +
> + /* Job done if page is free of the right migratetype */
> + if (!list_empty(&area->free_list[cc->migratetype]))
> + return COMPACT_PARTIAL;
> +
> + /* Job done if allocation would set block type */
> + if (cc->order >= pageblock_order && area->nr_free)
> return COMPACT_PARTIAL;
> - } else {
> - unsigned int order;
> - for (order = cc->order; order < MAX_ORDER; order++) {
> - struct free_area *area = &zone->free_area[cc->order];
> - /* Job done if page is free of the right migratetype */
> - if (!list_empty(&area->free_list[cc->migratetype]))
> - return COMPACT_PARTIAL;
> -
> - /* Job done if allocation would set block type */
> - if (cc->order >= pageblock_order && area->nr_free)
> - return COMPACT_PARTIAL;
> - }
> }
>
> return COMPACT_CONTINUE;
> @@ -921,60 +916,6 @@ unsigned long compaction_suitable(struct zone *zone, int order)
> return COMPACT_CONTINUE;
> }
>
> -static void compact_capture_page(struct compact_control *cc)
> -{
> - unsigned long flags;
> - int mtype, mtype_low, mtype_high;
> -
> - if (!cc->page || *cc->page)
> - return;
> -
> - /*
> - * For MIGRATE_MOVABLE allocations we capture a suitable page ASAP
> - * regardless of the migratetype of the freelist is is captured from.
> - * This is fine because the order for a high-order MIGRATE_MOVABLE
> - * allocation is typically at least a pageblock size and overall
> - * fragmentation is not impaired. Other allocation types must
> - * capture pages from their own migratelist because otherwise they
> - * could pollute other pageblocks like MIGRATE_MOVABLE with
> - * difficult to move pages and making fragmentation worse overall.
> - */
> - if (cc->migratetype == MIGRATE_MOVABLE) {
> - mtype_low = 0;
> - mtype_high = MIGRATE_PCPTYPES;
> - } else {
> - mtype_low = cc->migratetype;
> - mtype_high = cc->migratetype + 1;
> - }
> -
> - /* Speculatively examine the free lists without zone lock */
> - for (mtype = mtype_low; mtype < mtype_high; mtype++) {
> - int order;
> - for (order = cc->order; order < MAX_ORDER; order++) {
> - struct page *page;
> - struct free_area *area;
> - area = &(cc->zone->free_area[order]);
> - if (list_empty(&area->free_list[mtype]))
> - continue;
> -
> - /* Take the lock and attempt capture of the page */
> - if (!compact_trylock_irqsave(&cc->zone->lock, &flags, cc))
> - return;
> - if (!list_empty(&area->free_list[mtype])) {
> - page = list_entry(area->free_list[mtype].next,
> - struct page, lru);
> - if (capture_free_page(page, cc->order, mtype)) {
> - spin_unlock_irqrestore(&cc->zone->lock,
> - flags);
> - *cc->page = page;
> - return;
> - }
> - }
> - spin_unlock_irqrestore(&cc->zone->lock, flags);
> - }
> - }
> -}
> -
> static int compact_zone(struct zone *zone, struct compact_control *cc)
> {
> int ret;
> @@ -1054,9 +995,6 @@ static int compact_zone(struct zone *zone, struct compact_control *cc)
> goto out;
> }
> }
> -
> - /* Capture a page now if it is a suitable size */
> - compact_capture_page(cc);
> }
>
> out:
> @@ -1069,8 +1007,7 @@ out:
>
> static unsigned long compact_zone_order(struct zone *zone,
> int order, gfp_t gfp_mask,
> - bool sync, bool *contended,
> - struct page **page)
> + bool sync, bool *contended)
> {
> unsigned long ret;
> struct compact_control cc = {
> @@ -1080,7 +1017,6 @@ static unsigned long compact_zone_order(struct zone *zone,
> .migratetype = allocflags_to_migratetype(gfp_mask),
> .zone = zone,
> .sync = sync,
> - .page = page,
> };
> INIT_LIST_HEAD(&cc.freepages);
> INIT_LIST_HEAD(&cc.migratepages);
> @@ -1110,7 +1046,7 @@ int sysctl_extfrag_threshold = 500;
> */
> unsigned long try_to_compact_pages(struct zonelist *zonelist,
> int order, gfp_t gfp_mask, nodemask_t *nodemask,
> - bool sync, bool *contended, struct page **page)
> + bool sync, bool *contended)
> {
> enum zone_type high_zoneidx = gfp_zone(gfp_mask);
> int may_enter_fs = gfp_mask & __GFP_FS;
> @@ -1136,7 +1072,7 @@ unsigned long try_to_compact_pages(struct zonelist *zonelist,
> int status;
>
> status = compact_zone_order(zone, order, gfp_mask, sync,
> - contended, page);
> + contended);
> rc = max(status, rc);
>
> /* If a normal allocation would succeed, stop compacting */
> @@ -1192,7 +1128,6 @@ int compact_pgdat(pg_data_t *pgdat, int order)
> struct compact_control cc = {
> .order = order,
> .sync = false,
> - .page = NULL,
> };
>
> return __compact_pgdat(pgdat, &cc);
> @@ -1203,7 +1138,6 @@ static int compact_node(int nid)
> struct compact_control cc = {
> .order = -1,
> .sync = true,
> - .page = NULL,
> };
>
> return __compact_pgdat(NODE_DATA(nid), &cc);
> diff --git a/mm/internal.h b/mm/internal.h
> index d597f94..9ba2110 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -135,7 +135,6 @@ struct compact_control {
> int migratetype; /* MOVABLE, RECLAIMABLE etc */
> struct zone *zone;
> bool contended; /* True if a lock was contended */
> - struct page **page; /* Page captured of requested size */
> };
>
> unsigned long
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 4ba5e37..7e4ae85 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1389,14 +1389,8 @@ void split_page(struct page *page, unsigned int order)
> set_page_refcounted(page + i);
> }
>
> -/*
> - * Similar to the split_page family of functions except that the page
> - * required at the given order and being isolated now to prevent races
> - * with parallel allocators
> - */
> -int capture_free_page(struct page *page, int alloc_order, int migratetype)
> +static int __isolate_free_page(struct page *page, unsigned int order)
> {
> - unsigned int order;
> unsigned long watermark;
> struct zone *zone;
> int mt;
> @@ -1404,7 +1398,6 @@ int capture_free_page(struct page *page, int alloc_order, int migratetype)
> BUG_ON(!PageBuddy(page));
>
> zone = page_zone(page);
> - order = page_order(page);
> mt = get_pageblock_migratetype(page);
>
> if (mt != MIGRATE_ISOLATE) {
> @@ -1413,7 +1406,7 @@ int capture_free_page(struct page *page, int alloc_order, int migratetype)
> if (!zone_watermark_ok(zone, 0, watermark, 0, 0))
> return 0;
>
> - __mod_zone_freepage_state(zone, -(1UL << alloc_order), mt);
> + __mod_zone_freepage_state(zone, -(1UL << order), mt);
> }
>
> /* Remove page from free list */
> @@ -1421,11 +1414,7 @@ int capture_free_page(struct page *page, int alloc_order, int migratetype)
> zone->free_area[order].nr_free--;
> rmv_page_order(page);
>
> - if (alloc_order != order)
> - expand(zone, page, alloc_order, order,
> - &zone->free_area[order], migratetype);
> -
> - /* Set the pageblock if the captured page is at least a pageblock */
> + /* Set the pageblock if the isolated page is at least a pageblock */
> if (order >= pageblock_order - 1) {
> struct page *endpage = page + (1 << order) - 1;
> for (; page < endpage; page += pageblock_nr_pages) {
> @@ -1436,7 +1425,7 @@ int capture_free_page(struct page *page, int alloc_order, int migratetype)
> }
> }
>
> - return 1UL << alloc_order;
> + return 1UL << order;
> }
>
> /*
> @@ -1454,10 +1443,9 @@ int split_free_page(struct page *page)
> unsigned int order;
> int nr_pages;
>
> - BUG_ON(!PageBuddy(page));
> order = page_order(page);
>
> - nr_pages = capture_free_page(page, order, 0);
> + nr_pages = __isolate_free_page(page, order);
> if (!nr_pages)
> return 0;
>
> @@ -2163,8 +2151,6 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
> bool *contended_compaction, bool *deferred_compaction,
> unsigned long *did_some_progress)
> {
> - struct page *page = NULL;
> -
> if (!order)
> return NULL;
>
> @@ -2176,16 +2162,12 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
> current->flags |= PF_MEMALLOC;
> *did_some_progress = try_to_compact_pages(zonelist, order, gfp_mask,
> nodemask, sync_migration,
> - contended_compaction, &page);
> + contended_compaction);
> current->flags &= ~PF_MEMALLOC;
>
> - /* If compaction captured a page, prep and use it */
> - if (page) {
> - prep_new_page(page, order, gfp_mask);
> - goto got_page;
> - }
> -
> if (*did_some_progress != COMPACT_SKIPPED) {
> + struct page *page;
> +
> /* Page migration frees to the PCP lists but we want merging */
> drain_pages(get_cpu());
> put_cpu();
> @@ -2195,7 +2177,6 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
> alloc_flags & ~ALLOC_NO_WATERMARKS,
> preferred_zone, migratetype);
> if (page) {
> -got_page:
> preferred_zone->compact_blockskip_flush = false;
> preferred_zone->compact_considered = 0;
> preferred_zone->compact_defer_shift = 0;
>
> --
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--
Simon Jeons <simon.jeons@gmail.com>



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