From: Michal Hocko <mhocko@suse.com>
To: Rik van Riel <riel@surriel.com>
Cc: Hugh Dickins <hughd@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
kernel-team@fb.com, Mel Gorman <mgorman@suse.de>,
Andrea Arcangeli <aarcange@redhat.com>,
Matthew Wilcox <willy@infradead.org>
Subject: Re: [PATCH] mm,thp,shmem: limit shmem THP alloc gfp_mask
Date: Thu, 22 Oct 2020 10:15:32 +0200 [thread overview]
Message-ID: <20201022081532.GJ23790@dhcp22.suse.cz> (raw)
In-Reply-To: <20201021234846.5cc97e62@imladris.surriel.com>
On Wed 21-10-20 23:48:46, Rik van Riel wrote:
> The allocation flags of anonymous transparent huge pages can be controlled
> through the files in /sys/kernel/mm/transparent_hugepage/defrag, which can
> help the system from getting bogged down in the page reclaim and compaction
> code when many THPs are getting allocated simultaneously.
>
> However, the gfp_mask for shmem THP allocations were not limited by those
> configuration settings, and some workloads ended up with all CPUs stuck
> on the LRU lock in the page reclaim code, trying to allocate dozens of
> THPs simultaneously.
>
> This patch applies the same configurated limitation of THPs to shmem
> hugepage allocations, to prevent that from happening.
>
> This way a THP defrag setting of "never" or "defer+madvise" will result
> in quick allocation failures without direct reclaim when no 2MB free
> pages are available.
I remmeber I wanted to unify this in the past as well. The patch got
reverted in the end. It was a long story and I do not have time to read
through lengthy discussions again. I do remember though that there were
some objections pointing out that shmem has its own behavior which is
controlled by the mount option - at least for the explicitly mounted
shmems. I might misremember.
[...]
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 537c137698f8..d1290eb508e5 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1545,8 +1545,11 @@ static struct page *shmem_alloc_hugepage(gfp_t gfp,
> return NULL;
>
> shmem_pseudo_vma_init(&pvma, info, hindex);
> - page = alloc_pages_vma(gfp | __GFP_COMP | __GFP_NORETRY | __GFP_NOWARN,
> - HPAGE_PMD_ORDER, &pvma, 0, numa_node_id(), true);
> + /* Limit the gfp mask according to THP configuration. */
> + gfp |= __GFP_COMP | __GFP_NORETRY | __GFP_NOWARN;
What is the reason for these when alloc_hugepage_direct_gfpmask provides
the full mask?
> + gfp &= alloc_hugepage_direct_gfpmask(&pvma);
> + page = alloc_pages_vma(gfp, HPAGE_PMD_ORDER, &pvma, 0, numa_node_id(),
> + true);
> shmem_pseudo_vma_destroy(&pvma);
> if (page)
> prep_transhuge_page(page);
>
> --
> All rights reversed.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2020-10-22 8:15 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-22 3:48 [PATCH] mm,thp,shmem: limit shmem THP alloc gfp_mask Rik van Riel
2020-10-22 8:15 ` Michal Hocko [this message]
2020-10-22 13:25 ` Rik van Riel
2020-10-22 15:50 ` Michal Hocko
2020-10-22 16:06 ` Rik van Riel
2020-10-23 6:47 ` Michal Hocko
2020-10-22 14:51 ` Vlastimil Babka
2020-10-22 14:52 ` Vlastimil Babka
2020-10-22 16:00 ` Yu Xu
2020-10-22 16:40 ` Rik van Riel
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