lkml.org 
[lkml]   [2022]   [Jan]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH RFC v2 1/9] mm: optimize do_wp_page() for exclusive pages in the swapcache
    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>

    \
     
     \ /
      Last update: 2022-01-26 15:25    [W:4.734 / U:0.768 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site