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From: David Hildenbrand <david@redhat.com>
To: Yang Shi <yang.shi@linux.alibaba.com>,
	willy@infradead.org, mhocko@suse.com, akpm@linux-foundation.org
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm: migrate.c: migrate PG_readahead flag
Date: Fri, 14 Feb 2020 11:04:22 +0100	[thread overview]
Message-ID: <5178c119-778a-7a17-e047-6954cb00d4a0@redhat.com> (raw)
In-Reply-To: <1581640185-95731-1-git-send-email-yang.shi@linux.alibaba.com>

On 14.02.20 01:29, Yang Shi wrote:
> Currently migration code doesn't migrate PG_readahead flag.
> Theoretically this would incur slight performance loss as the
> application might have to ramp its readahead back up again.  Even though
> such problem happens, it might be hidden by something else since
> migration is typically triggered by compaction and NUMA balancing, any
> of which should be more noticeable.
> 
> Migrate the flag after end_page_writeback() since it may clear
> PG_reclaim flag, which is the same bit as PG_readahead, for the new
> page.
> 
> Cc: Matthew Wilcox <willy@infradead.org>
> Cc: Michal Hocko <mhocko@suse.com>
> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com>
> ---
> I didn't experience any real problem, found by visual inspection. And, this was
> discussed in thread: https://lore.kernel.org/linux-mm/185ce762-f25d-a013-6daa-8c288f1ff791@linux.alibaba.com/T/#m1977ce1de513401b7d09d6fa14fcffe849580aae
> 
>  mm/migrate.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/mm/migrate.c b/mm/migrate.c
> index edf42ed..f3c492d 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -647,6 +647,14 @@ void migrate_page_states(struct page *newpage, struct page *page)
>  	if (PageWriteback(newpage))
>  		end_page_writeback(newpage);
>  
> +	/*
> +	 * PG_readahead share the same bit with PG_reclaim, the above
> +	 * end_page_writeback() may clear PG_readahead mistakenly, so set
> +	 * the bit after that.
> +	 */
> +	if (PageReadahead(page))
> +		SetPageReadahead(newpage);
> +
>  	copy_page_owner(page, newpage);
>  
>  	mem_cgroup_migrate(page, newpage);
> 

Looks good to me!

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Thanks,

David / dhildenb



      parent reply	other threads:[~2020-02-14 10:04 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-14  0:29 [PATCH] mm: migrate.c: migrate PG_readahead flag Yang Shi
2020-02-14  2:55 ` Andrew Morton
2020-02-14  3:58   ` Yang Shi
2020-02-14  4:07     ` Matthew Wilcox
2020-02-14  8:34 ` Michal Hocko
2020-02-14 10:04 ` David Hildenbrand [this message]

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