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SubjectRe: Free memory never fully used, swapping
> There are actually a few problems here.  I think they are worth looking
> at them separately, unless "don't use order 3 allocations" is a valid
> statement, in which case we should fix slub.
> The funny thing here is that slub.c's allocate_slab() calls alloc_pages()
> with flags | __GFP_NOWARN | __GFP_NORETRY, and intentionally tries a
> lower order allocation automatically if it fails. This is why there is
> no allocation failure warning when this happens. However, it is too late
> -- kswapd is woken and it ties to bring order 3 up to the watermark.
> If we hacked __alloc_pages_slowpath() to not wake kswapd when
> __GFP_NOWARN is set, we would never see this problem and the slub
> optimization might still mostly work. Either way, we should "fix" slub
> or "fix" order-3 allocations, so that other people who are using slub
> don't hit the same problem.


Subject: [PATCH] slub: use no __GFP_WAIT instead __GFP_NORETRY

mm/slub.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 8c66aef..0c77399 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1134,7 +1134,7 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node)
* Let the initial higher-order allocation fail under memory pressure
* so we fall-back to the minimum order allocation.
- alloc_gfp = (flags | __GFP_NOWARN | __GFP_NORETRY) & ~__GFP_NOFAIL;
+ alloc_gfp = (flags | __GFP_NOWARN) & ~(__GFP_NOFAIL | __GFP_WAIT);

page = alloc_slab_page(alloc_gfp, node, oo);
if (unlikely(!page)) {

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