The patch titled
Subject: mm: memcontrol: do not kill uncharge batching in free_pages_and_swap_cache
has been added to the -mm tree. Its filename is
mm-memcontrol-do-not-kill-uncharge-batching-in-free_pages_and_swap_cache.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-memcontrol-do-not-kill-uncharge-batching-in-free_pages_and_swap_cache.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-memcontrol-do-not-kill-uncharge-batching-in-free_pages_and_swap_cache.patch
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------------------------------------------------------
From: Michal Hocko <mhocko@xxxxxxx>
Subject: mm: memcontrol: do not kill uncharge batching in free_pages_and_swap_cache
free_pages_and_swap_cache limits release_pages to PAGEVEC_SIZE chunks.
This is not a big deal for the normal release path but it completely kills
memcg uncharge batching which reduces res_counter spin_lock contention.
Dave has noticed this with his page fault scalability test case on a large
machine when the lock was basically dominating on all CPUs:
80.18% 80.18% [kernel] [k] _raw_spin_lock
|
--- _raw_spin_lock
|
|--66.59%-- res_counter_uncharge_until
| res_counter_uncharge
| uncharge_batch
| uncharge_list
| mem_cgroup_uncharge_list
| release_pages
| free_pages_and_swap_cache
| tlb_flush_mmu_free
| |
| |--90.12%-- unmap_single_vma
| | unmap_vmas
| | unmap_region
| | do_munmap
| | vm_munmap
| | sys_munmap
| | system_call_fastpath
| | __GI___munmap
| |
| --9.88%-- tlb_flush_mmu
| tlb_finish_mmu
| unmap_region
| do_munmap
| vm_munmap
| sys_munmap
| system_call_fastpath
| __GI___munmap
In his case the load was running in the root memcg and that part has been
handled by reverting 05b843012335 ("mm: memcontrol: use root_mem_cgroup
res_counter") because this is a clear regression, but the problem remains
inside dedicated memcgs.
There is no reason to limit release_pages to PAGEVEC_SIZE batches other
than lru_lock held times. This logic, however, can be moved inside the
function. mem_cgroup_uncharge_list and free_hot_cold_page_list do not
hold any lock for the whole pages_to_free list so it is safe to call them
in a single run.
Page reference count and LRU handling is moved to release_lru_pages and
that is run in PAGEVEC_SIZE batches.
Signed-off-by: Michal Hocko <mhocko@xxxxxxx>
Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Reported-by: Dave Hansen <dave@xxxxxxxx>
Cc: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
Cc: Greg Thelen <gthelen@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/swap.c | 27 +++++++++++++++++++++------
mm/swap_state.c | 14 ++++----------
2 files changed, 25 insertions(+), 16 deletions(-)
diff -puN mm/swap.c~mm-memcontrol-do-not-kill-uncharge-batching-in-free_pages_and_swap_cache mm/swap.c
--- a/mm/swap.c~mm-memcontrol-do-not-kill-uncharge-batching-in-free_pages_and_swap_cache
+++ a/mm/swap.c
@@ -888,9 +888,9 @@ void lru_add_drain_all(void)
}
/*
- * Batched page_cache_release(). Decrement the reference count on all the
- * passed pages. If it fell to zero then remove the page from the LRU and
- * free it.
+ * Batched lru release. Decrement the reference count on all the passed pages.
+ * If it fell to zero then remove the page from the LRU and add it to the given
+ * list to be freed by the caller.
*
* Avoid taking zone->lru_lock if possible, but if it is taken, retain it
* for the remainder of the operation.
@@ -900,10 +900,10 @@ void lru_add_drain_all(void)
* grabbed the page via the LRU. If it did, give up: shrink_inactive_list()
* will free it.
*/
-void release_pages(struct page **pages, int nr, bool cold)
+static void release_lru_pages(struct page **pages, int nr,
+ struct list_head *pages_to_free)
{
int i;
- LIST_HEAD(pages_to_free);
struct zone *zone = NULL;
struct lruvec *lruvec;
unsigned long uninitialized_var(flags);
@@ -943,11 +943,26 @@ void release_pages(struct page **pages,
/* Clear Active bit in case of parallel mark_page_accessed */
__ClearPageActive(page);
- list_add(&page->lru, &pages_to_free);
+ list_add(&page->lru, pages_to_free);
}
if (zone)
spin_unlock_irqrestore(&zone->lru_lock, flags);
+}
+/*
+ * Batched page_cache_release(). Frees and uncharges all given pages
+ * for which the reference count drops to 0.
+ */
+void release_pages(struct page **pages, int nr, bool cold)
+{
+ LIST_HEAD(pages_to_free);
+ while (nr) {
+ int batch = min(nr, PAGEVEC_SIZE);
+
+ release_lru_pages(pages, batch, &pages_to_free);
+ pages += batch;
+ nr -= batch;
+ }
mem_cgroup_uncharge_list(&pages_to_free);
free_hot_cold_page_list(&pages_to_free, cold);
}
diff -puN mm/swap_state.c~mm-memcontrol-do-not-kill-uncharge-batching-in-free_pages_and_swap_cache mm/swap_state.c
--- a/mm/swap_state.c~mm-memcontrol-do-not-kill-uncharge-batching-in-free_pages_and_swap_cache
+++ a/mm/swap_state.c
@@ -265,18 +265,12 @@ void free_page_and_swap_cache(struct pag
void free_pages_and_swap_cache(struct page **pages, int nr)
{
struct page **pagep = pages;
+ int i;
lru_add_drain();
- while (nr) {
- int todo = min(nr, PAGEVEC_SIZE);
- int i;
-
- for (i = 0; i < todo; i++)
- free_swap_cache(pagep[i]);
- release_pages(pagep, todo, false);
- pagep += todo;
- nr -= todo;
- }
+ for (i = 0; i < nr; i++)
+ free_swap_cache(pagep[i]);
+ release_pages(pagep, nr, false);
}
/*
_
Patches currently in -mm which might be from mhocko@xxxxxxx are
introduce-dump_vma.patch
introduce-dump_vma-fix.patch
introduce-vm_bug_on_vma.patch
convert-a-few-vm_bug_on-callers-to-vm_bug_on_vma.patch
mm-debug-mm-introduce-vm_bug_on_mm-fixpatch.patch
mm-debug-mm-introduce-vm_bug_on_mm-fix-fixpatch.patch
mm-debug-mm-introduce-vm_bug_on_mm-fix-fixpatch-fix.patch
memcg-move-memcg_allocfree_cache_params-to-slab_commonc.patch
memcg-dont-call-memcg_update_all_caches-if-new-cache-id-fits.patch
memcg-move-memcg_update_cache_size-to-slab_commonc.patch
mm-memcontrol-do-not-kill-uncharge-batching-in-free_pages_and_swap_cache.patch
mm-memcontrol-simplify-detecting-when-the-memoryswap-limit-is-hit.patch
mm-memcontrol-fix-transparent-huge-page-allocations-under-pressure.patch
linux-next.patch
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