linux-kernel - Re: [PATCH 04/12] mm, thp, tmpfs: split huge page when moving from page cache to swap

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Message-ID: <CACz4_2eoRoyUU1G3veS=veWTi1HtPrgLQK0tyXONXcQj1Xi4EQ@mail.gmail.com>
Date:	Tue, 15 Oct 2013 12:00:03 -0700
From:	Ning Qu <quning@...gle.com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Wu Fengguang <fengguang.wu@...el.com>, Jan Kara <jack@...e.cz>,
	Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
	Andi Kleen <ak@...ux.intel.com>,
	Matthew Wilcox <willy@...ux.intel.com>,
	Hillf Danton <dhillf@...il.com>, Dave Hansen <dave@...1.net>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 04/12] mm, thp, tmpfs: split huge page when moving from
 page cache to swap

Let me take another look at that logic. Thanks!
Best wishes,
-- 
Ning Qu (曲宁) | Software Engineer | quning@...gle.com | +1-408-418-6066


On Tue, Oct 15, 2013 at 3:33 AM, Kirill A. Shutemov
<kirill.shutemov@...ux.intel.com> wrote:
> Ning Qu wrote:
>> in shmem_writepage, we have to split the huge page when moving pages
>> from page cache to swap because we don't support huge page in swap
>> yet.
>>
>> Signed-off-by: Ning Qu <quning@...il.com>
>> ---
>>  mm/shmem.c | 9 ++++++++-
>>  1 file changed, 8 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/shmem.c b/mm/shmem.c
>> index 8fe17dd..68a0e1d 100644
>> --- a/mm/shmem.c
>> +++ b/mm/shmem.c
>> @@ -898,6 +898,13 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
>>       swp_entry_t swap;
>>       pgoff_t index;
>>
>> +     /* TODO: we have to break the huge page at this point,
>> +      * since we have no idea how to recover a huge page from
>> +      * swap.
>> +      */
>> +     if (PageTransCompound(page))
>> +             split_huge_page(compound_trans_head(page));
>> +
>
> After the split you handle here only first small page of the huge page.
> Is it what we want to do? Should we swap out all small pages of the huge
> page?
>
> --
>  Kirill A. Shutemov
--
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