The patch titled
Subject: mm, page_frag: recover from memory pressure
has been added to the -mm tree. Its filename is
page_frag-recover-from-memory-pressure.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/page_frag-recover-from-memory-pressure.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/page_frag-recover-from-memory-pressure.patch
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: Dongli Zhang <dongli.zhang@xxxxxxxxxx>
Subject: mm, page_frag: recover from memory pressure
The ethernet driver may allocate skb (and skb->data) via napi_alloc_skb().
This ends up to page_frag_alloc() to allocate skb->data from
page_frag_cache->va.
During the memory pressure, page_frag_cache->va may be allocated as
pfmemalloc page. As a result, the skb->pfmemalloc is always true as
skb->data is from page_frag_cache->va. The skb will be dropped if the
sock (receiver) does not have SOCK_MEMALLOC. This is expected behaviour
under memory pressure.
However, once kernel is not under memory pressure any longer (suppose
large amount of memory pages are just reclaimed), the page_frag_alloc()
may still re-use the prior pfmemalloc page_frag_cache->va to allocate
skb->data. As a result, the skb->pfmemalloc is always true unless
page_frag_cache->va is re-allocated, even if the kernel is not under
memory pressure any longer.
Here is how kernel runs into issue.
1. The kernel is under memory pressure and allocation of
PAGE_FRAG_CACHE_MAX_ORDER in __page_frag_cache_refill() will fail.
Instead, the pfmemalloc page is allocated for page_frag_cache->va.
2. All skb->data from page_frag_cache->va (pfmemalloc) will have
skb->pfmemalloc=true. The skb will always be dropped by sock without
SOCK_MEMALLOC. This is an expected behaviour.
3. Suppose a large amount of pages are reclaimed and kernel is not
under memory pressure any longer. We expect skb->pfmemalloc drop will
not happen.
4. Unfortunately, page_frag_alloc() does not proactively re-allocate
page_frag_alloc->va and will always re-use the prior pfmemalloc page.
The skb->pfmemalloc is always true even kernel is not under memory
pressure any longer.
Fix this by freeing and re-allocating the page instead of recycling it.
Link: https://lore.kernel.org/lkml/20201103193239.1807-1-dongli.zhang@xxxxxxxxxx/
Link: https://lore.kernel.org/linux-mm/20201105042140.5253-1-willy@xxxxxxxxxxxxx/
Link: https://lkml.kernel.org/r/20201115201029.11903-1-dongli.zhang@xxxxxxxxxx
Fixes: 79930f5892e ("net: do not deplete pfmemalloc reserve")
Signed-off-by: Dongli Zhang <dongli.zhang@xxxxxxxxxx>
Suggested-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: Aruna Ramakrishna <aruna.ramakrishna@xxxxxxxxxx>
Cc: Bert Barbe <bert.barbe@xxxxxxxxxx>
Cc: Rama Nichanamatlu <rama.nichanamatlu@xxxxxxxxxx>
Cc: Venkat Venkatsubra <venkat.x.venkatsubra@xxxxxxxxxx>
Cc: Manjunath Patil <manjunath.b.patil@xxxxxxxxxx>
Cc: Joe Jin <joe.jin@xxxxxxxxxx>
Cc: SRINIVAS <srinivas.eeda@xxxxxxxxxx>
Cc: David S. Miller <davem@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 5 +++++
1 file changed, 5 insertions(+)
--- a/mm/page_alloc.c~page_frag-recover-from-memory-pressure
+++ a/mm/page_alloc.c
@@ -5103,6 +5103,11 @@ refill:
if (!page_ref_sub_and_test(page, nc->pagecnt_bias))
goto refill;
+ if (unlikely(nc->pfmemalloc)) {
+ free_the_page(page, compound_order(page));
+ goto refill;
+ }
+
#if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE)
/* if size can vary use size else just use PAGE_SIZE */
size = nc->size;
_
Patches currently in -mm which might be from dongli.zhang@xxxxxxxxxx are
page_frag-recover-from-memory-pressure.patch
