From: Davidlohr Bueso <dave@stgolabs.net>
To: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>,
linux-mm@kvack.org, Petr Holasek <pholasek@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 1/5] mm: add cond_resched() to the rmap walks
Date: Mon, 2 Nov 2015 12:31:28 -0800 [thread overview]
Message-ID: <20151102203128.GC1707@linux-uzut.site> (raw)
In-Reply-To: <1446483691-8494-2-git-send-email-aarcange@redhat.com>
On Mon, 02 Nov 2015, Andrea Arcangeli wrote:
>The rmap walk must reach every possible mapping of the page, so if a
>page is heavily shared (no matter if it's KSM, anon, pagecache) there
>will be tons of entries to walk through. All optimizations with
>prio_tree, anon_vma chains, interval tree, helps to find the right
>virtual mapping faster, but if there are lots of virtual mappings, all
>mapping must still be walked through.
>
>The biggest cost is for the IPIs, but regardless of the IPIs, it's
>generally safer to keep these cond_resched() in all cases, as even if
>we massively reduce the number of IPIs, the number of entries to walk
>IPI-less may still be large and no entry can be possibly skipped in
>the page migration case.
>
>Acked-by: Hugh Dickins <hughd@google.com>
>Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Davidlohr Bueso <dbueso@suse.de>
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next prev parent reply other threads:[~2015-11-02 20:31 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-02 17:01 [PATCH 0/5] KSM updates v2 Andrea Arcangeli
2015-11-02 17:01 ` [PATCH 1/5] mm: add cond_resched() to the rmap walks Andrea Arcangeli
2015-11-02 20:31 ` Davidlohr Bueso [this message]
2015-11-02 17:01 ` [PATCH 2/5] ksm: don't fail stable tree lookups if walking over stale stable_nodes Andrea Arcangeli
2015-11-02 17:01 ` [PATCH 3/5] ksm: use the helper method to do the hlist_empty check Andrea Arcangeli
2015-11-02 17:01 ` [PATCH 4/5] ksm: use find_mergeable_vma in try_to_merge_with_ksm_page Andrea Arcangeli
2015-11-02 17:01 ` [PATCH 5/5] ksm: unstable_tree_search_insert error checking cleanup Andrea Arcangeli
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