From: Vlastimil Babka <vbabka@suse.cz>
To: David Hildenbrand <david@redhat.com>, linux-kernel@vger.kernel.org
Cc: 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>,
Matthew Wilcox <willy@infradead.org>,
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
Subject: Re: [PATCH v3 2/9] mm: optimize do_wp_page() for fresh pages in local LRU pagevecs
Date: Wed, 9 Mar 2022 18:53:23 +0100 [thread overview]
Message-ID: <feccf0e4-61c4-3292-bd87-ff59c4fa0ec6@suse.cz> (raw)
In-Reply-To: <20220131162940.210846-3-david@redhat.com>
On 1/31/22 17:29, David Hildenbrand wrote:
> For example, if a page just got swapped in via a read fault, the LRU
> pagevecs might still hold a reference to the page. If we trigger a
> write fault on such a page, the additional reference from the LRU
> pagevecs will prohibit reusing the page.
>
> Let's conditionally drain the local LRU pagevecs when we stumble over a
> !PageLRU() page. We cannot easily drain remote LRU pagevecs and it might
> not be desirable performance-wise. Consequently, this will only avoid
> copying in some cases.
>
> Add a simple "page_count(page) > 3" check first but keep the
> "page_count(page) > 1 + PageSwapCache(page)" check in place, as
> we want to minimize cases where we remove a page from the swapcache but
> won't be able to reuse it, for example, because another process has it
> mapped R/O, to not affect reclaim.
>
> We cannot easily handle the following cases and we will always have to
> copy:
>
> (1) The page is referenced in the LRU pagevecs of other CPUs. We really
> would have to drain the LRU pagevecs of all CPUs -- most probably
> copying is much cheaper.
>
> (2) The page is already PageLRU() but is getting moved between LRU
> lists, for example, for activation (e.g., mark_page_accessed()),
> deactivation (MADV_COLD), or lazyfree (MADV_FREE). We'd have to
> drain mostly unconditionally, which might be bad performance-wise.
> Most probably this won't happen too often in practice.
>
> Note that there are other reasons why an anon page might temporarily not
> be PageLRU(): for example, compaction and migration have to isolate LRU
> pages from the LRU lists first (isolate_lru_page()), moving them to
> temporary local lists and clearing PageLRU() and holding an additional
> reference on the page. In that case, we'll always copy.
>
> This change seems to be fairly effective with the reproducer [1] shared
> by Nadav, as long as writeback is done synchronously, for example, using
> zram. However, with asynchronous writeback, we'll usually fail to free the
> swapcache because the page is still under writeback: something we cannot
> easily optimize for, and maybe it's not really relevant in practice.
>
> [1] https://lkml.kernel.org/r/0480D692-D9B2-429A-9A88-9BBA1331AC3A@gmail.com
>
> Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
next prev parent reply other threads:[~2022-03-09 17:53 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-31 16:29 [PATCH v3 0/9] mm: COW fixes part 1: fix the COW security issue for THP and swap David Hildenbrand
2022-01-31 16:29 ` [PATCH v3 1/9] mm: optimize do_wp_page() for exclusive pages in the swapcache David Hildenbrand
2022-01-31 16:29 ` [PATCH v3 2/9] mm: optimize do_wp_page() for fresh pages in local LRU pagevecs David Hildenbrand
2022-03-09 17:53 ` Vlastimil Babka [this message]
2022-01-31 16:29 ` [PATCH v3 3/9] mm: slightly clarify KSM logic in do_swap_page() David Hildenbrand
2022-03-09 18:03 ` Vlastimil Babka
2022-03-09 18:48 ` Yang Shi
2022-03-09 19:15 ` David Hildenbrand
2022-03-09 20:50 ` Andrew Morton
2022-01-31 16:29 ` [PATCH v3 4/9] mm: streamline COW " David Hildenbrand
2022-03-10 9:41 ` Vlastimil Babka
2022-01-31 16:29 ` [PATCH v3 5/9] mm/huge_memory: streamline COW logic in do_huge_pmd_wp_page() David Hildenbrand
2022-03-10 9:52 ` Vlastimil Babka
2022-01-31 16:29 ` [PATCH v3 6/9] mm/khugepaged: remove reuse_swap_page() usage David Hildenbrand
2022-02-01 21:31 ` Yang Shi
2022-03-10 10:37 ` Vlastimil Babka
2022-01-31 16:29 ` [PATCH v3 7/9] mm/swapfile: remove stale reuse_swap_page() David Hildenbrand
2022-02-02 14:35 ` Christoph Hellwig
2022-02-02 17:01 ` David Hildenbrand
2022-03-10 10:44 ` Vlastimil Babka
2022-01-31 16:29 ` [PATCH v3 8/9] mm/huge_memory: remove stale page_trans_huge_mapcount() David Hildenbrand
2022-03-10 10:50 ` Vlastimil Babka
2022-01-31 16:29 ` [PATCH v3 9/9] mm/huge_memory: remove stale locking logic from __split_huge_pmd() David Hildenbrand
2022-03-10 11:02 ` Vlastimil Babka
2022-02-01 18:59 ` [PATCH v3 0/9] mm: COW fixes part 1: fix the COW security issue for THP and swap Linus Torvalds
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