Message-ID: <54E1D977.30004@suse.cz>
Date: Mon, 16 Feb 2015 12:50:15 +0100
From: Vlastimil Babka <vbabka@suse.cz>
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To: Ebru Akagunduz <ebru.akagunduz@gmail.com>, linux-mm@kvack.org
CC: akpm@linux-foundation.org, kirill@shutemov.name, mhocko@suse.cz,
        mgorman@suse.de, rientjes@google.com, sasha.levin@oracle.com,
        hughd@google.com, hannes@cmpxchg.org, linux-kernel@vger.kernel.org,
        riel@redhat.com, aarcange@redhat.com
Subject: Re: [PATCH v2] mm: incorporate zero pages into transparent huge pages
References: <1423688635-4306-1-git-send-email-ebru.akagunduz@gmail.com>
In-Reply-To: <1423688635-4306-1-git-send-email-ebru.akagunduz@gmail.com>
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On 02/11/2015 10:03 PM, Ebru Akagunduz wrote:
> This patch improves THP collapse rates, by allowing zero pages.
> 
> Currently THP can collapse 4kB pages into a THP when there
> are up to khugepaged_max_ptes_none pte_none ptes in a 2MB
> range.  This patch counts pte none and mapped zero pages
> with the same variable.
> 
> The patch was tested with a program that allocates 800MB of
> memory, and performs interleaved reads and writes, in a pattern
> that causes some 2MB areas to first see read accesses, resulting
> in the zero pfn being mapped there.
> 
> To simulate memory fragmentation at allocation time, I modified
> do_huge_pmd_anonymous_page to return VM_FAULT_FALLBACK for read
> faults.
> 
> Without the patch, only %50 of the program was collapsed into
> THP and the percentage did not increase over time.
> 
> With this patch after 10 minutes of waiting khugepaged had
> collapsed %99 of the program's memory.
> 
> Signed-off-by: Ebru Akagunduz <ebru.akagunduz@gmail.com>
> Reviewed-by: Rik van Riel <riel@redhat.com>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

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