linux-kernel - Re: [PATCH] z3fold: remove the unnecessary limit in z3fold_compact

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Date:   Mon, 17 Oct 2016 09:51:16 +0800
From:   zhong jiang <zhongjiang@...wei.com>
To:     Vitaly Wool <vitalywool@...il.com>
CC:     Dave Chinner <david@...morbit.com>,
        Seth Jennings <sjenning@...hat.com>,
        Dan Streetman <ddstreet@...e.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] z3fold: remove the unnecessary limit in z3fold_compact_page

On 2016/10/15 3:25, Vitaly Wool wrote:
> On Fri, Oct 14, 2016 at 3:35 PM, zhongjiang <zhongjiang@...wei.com> wrote:
>> From: zhong jiang <zhongjiang@...wei.com>
>>
>> z3fold compact page has nothing with the last_chunks. even if
>> last_chunks is not free, compact page will proceed.
>>
>> The patch just remove the limit without functional change.
>>
>> Signed-off-by: zhong jiang <zhongjiang@...wei.com>
>> ---
>>  mm/z3fold.c | 3 +--
>>  1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/mm/z3fold.c b/mm/z3fold.c
>> index e8fc216..4668e1c 100644
>> --- a/mm/z3fold.c
>> +++ b/mm/z3fold.c
>> @@ -258,8 +258,7 @@ static int z3fold_compact_page(struct z3fold_header *zhdr)
>>
>>
>>         if (!test_bit(MIDDLE_CHUNK_MAPPED, &page->private) &&
>> -           zhdr->middle_chunks != 0 &&
>> -           zhdr->first_chunks == 0 && zhdr->last_chunks == 0) {
>> +           zhdr->middle_chunks != 0 && zhdr->first_chunks == 0) {
>>                 memmove(beg + ZHDR_SIZE_ALIGNED,
>>                         beg + (zhdr->start_middle << CHUNK_SHIFT),
>>                         zhdr->middle_chunks << CHUNK_SHIFT);
> This check is actually important because if we move the middle chunk
> to the first and leave the last chunk, handles will become invalid and
> there won't be any easy way to fix that.
>
> Best regards,
>    Vitaly
>
> .
>
 Thanks for you reply. you are right. Leave the last chunk to compact will
 lead to the first_num increase. Thus, handle_to_buddy will become invalid.

 Thanks
 zhongjiang