From: Matthew Wilcox <willy@infradead.org>
To: David Hildenbrand <david@redhat.com>
Cc: linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Hugh Dickins <hughd@google.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
David Rientjes <rientjes@google.com>,
Shakeel Butt <shakeelb@google.com>,
John Hubbard <jhubbard@nvidia.com>,
Jason Gunthorpe <jgg@nvidia.com>,
Mike Kravetz <mike.kravetz@oracle.com>,
Mike Rapoport <rppt@linux.ibm.com>,
Yang Shi <shy828301@gmail.com>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
Vlastimil Babka <vbabka@suse.cz>, Jann Horn <jannh@google.com>,
Michal Hocko <mhocko@kernel.org>, Nadav Amit <namit@vmware.com>,
Rik van Riel <riel@surriel.com>, Roman Gushchin <guro@fb.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Peter Xu <peterx@redhat.com>, Donald Dutile <ddutile@redhat.com>,
Christoph Hellwig <hch@lst.de>, Oleg Nesterov <oleg@redhat.com>,
Jan Kara <jack@suse.cz>, Liang Zhang <zhangliang5@huawei.com>,
linux-mm@kvack.org, Nadav Amit <nadav.amit@gmail.com>
Subject: Re: [PATCH RFC v2 1/9] mm: optimize do_wp_page() for exclusive pages in the swapcache
Date: Wed, 26 Jan 2022 14:25:25 +0000 [thread overview]
Message-ID: <YfFZ1SruNMubhJLo@casper.infradead.org> (raw)
In-Reply-To: <20220126095557.32392-2-david@redhat.com>
On Wed, Jan 26, 2022 at 10:55:49AM +0100, David Hildenbrand wrote:
> Liang Zhang reported [1] that the current COW logic in do_wp_page() is
> sub-optimal when it comes to swap+read fault+write fault of anonymous
> pages that have a single user, visible via a performance degradation in
> the redis benchmark. Something similar was previously reported [2] by
> Nadav with a simple reproducer.
>
> Let's optimize for pages that have been added to the swapcache but only
> have an exclusive owner. Try removing the swapcache reference if there is
> hope that we're the exclusive user.
>
> We will fail removing the swapcache reference in two scenarios:
> (1) There are additional swap entries referencing the page: copying
> instead of reusing is the right thing to do.
> (2) The page is under writeback: theoretically we might be able to reuse
> in some cases, however, we cannot remove the additional reference
> and will have to copy.
>
> Further, we might have additional references from the LRU pagevecs,
> which will force us to copy instead of being able to reuse. We'll try
> handling such references for some scenarios next. Concurrent writeback
> cannot be handled easily and we'll always have to copy.
>
> While at it, remove the superfluous page_mapcount() check: it's
> implicitly covered by the page_count() for ordinary anon pages.
>
> [1] https://lkml.kernel.org/r/20220113140318.11117-1-zhangliang5@huawei.com
> [2] https://lkml.kernel.org/r/0480D692-D9B2-429A-9A88-9BBA1331AC3A@gmail.com
>
> Reported-by: Liang Zhang <zhangliang5@huawei.com>
> Reported-by: Nadav Amit <nadav.amit@gmail.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
next prev parent reply other threads:[~2022-01-26 14:25 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-26 9:55 [PATCH RFC v2 0/9] mm: COW fixes part 1: fix the COW security issue for THP and swap David Hildenbrand
2022-01-26 9:55 ` [PATCH RFC v2 1/9] mm: optimize do_wp_page() for exclusive pages in the swapcache David Hildenbrand
2022-01-26 14:25 ` Matthew Wilcox [this message]
2022-01-28 12:53 ` Vlastimil Babka
2022-01-28 13:44 ` David Hildenbrand
2022-01-26 9:55 ` [PATCH RFC v2 2/9] mm: optimize do_wp_page() for fresh pages in local LRU pagevecs David Hildenbrand
2022-01-26 14:31 ` Matthew Wilcox
2022-01-26 14:36 ` David Hildenbrand
2022-01-26 9:55 ` [PATCH RFC v2 3/9] mm: slightly clarify KSM logic in do_swap_page() David Hildenbrand
2022-01-26 9:55 ` [PATCH RFC v2 4/9] mm: streamline COW " David Hildenbrand
2022-01-26 9:55 ` [PATCH RFC v2 5/9] mm/huge_memory: streamline COW logic in do_huge_pmd_wp_page() David Hildenbrand
2022-01-26 20:36 ` Yang Shi
2022-01-27 8:14 ` David Hildenbrand
2022-01-26 9:55 ` [PATCH RFC v2 6/9] mm/khugepaged: remove reuse_swap_page() usage David Hildenbrand
2022-01-27 21:23 ` Yang Shi
2022-01-28 8:41 ` David Hildenbrand
2022-01-28 17:10 ` Yang Shi
2022-01-26 9:55 ` [PATCH RFC v2 7/9] mm/swapfile: remove reuse_swap_page() David Hildenbrand
2022-01-26 9:55 ` [PATCH RFC v2 8/9] mm/huge_memory: remove stale page_trans_huge_mapcount() David Hildenbrand
2022-01-26 9:55 ` [PATCH RFC v2 9/9] mm/huge_memory: remove stale locking logic from __split_huge_pmd() David Hildenbrand
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