linux-kernel - Re: [PATCH/RESEND v2 3/5] z3fold: extend compaction function

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Date:   Wed, 11 Jan 2017 17:43:13 +0100
From:   Vitaly Wool <vitalywool@...il.com>
To:     Dan Streetman <ddstreet@...e.org>
Cc:     Linux-MM <linux-mm@...ck.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH/RESEND v2 3/5] z3fold: extend compaction function

On Wed, Jan 11, 2017 at 5:28 PM, Dan Streetman <ddstreet@...e.org> wrote:
> On Wed, Jan 11, 2017 at 10:06 AM, Vitaly Wool <vitalywool@...il.com> wrote:
>> z3fold_compact_page() currently only handles the situation when
>> there's a single middle chunk within the z3fold page. However it
>> may be worth it to move middle chunk closer to either first or
>> last chunk, whichever is there, if the gap between them is big
>> enough.
>>
>> This patch adds the relevant code, using BIG_CHUNK_GAP define as
>> a threshold for middle chunk to be worth moving.
>>
>> Signed-off-by: Vitaly Wool <vitalywool@...il.com>
>> ---
>>  mm/z3fold.c | 26 +++++++++++++++++++++++++-
>>  1 file changed, 25 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/z3fold.c b/mm/z3fold.c
>> index 98ab01f..fca3310 100644
>> --- a/mm/z3fold.c
>> +++ b/mm/z3fold.c
>> @@ -268,6 +268,7 @@ static inline void *mchunk_memmove(struct z3fold_header *zhdr,
>>                        zhdr->middle_chunks << CHUNK_SHIFT);
>>  }
>>
>> +#define BIG_CHUNK_GAP  3
>>  /* Has to be called with lock held */
>>  static int z3fold_compact_page(struct z3fold_header *zhdr)
>>  {
>> @@ -286,8 +287,31 @@ static int z3fold_compact_page(struct z3fold_header *zhdr)
>>                 zhdr->middle_chunks = 0;
>>                 zhdr->start_middle = 0;
>>                 zhdr->first_num++;
>> +               return 1;
>>         }
>> -       return 1;
>> +
>> +       /*
>> +        * moving data is expensive, so let's only do that if
>> +        * there's substantial gain (at least BIG_CHUNK_GAP chunks)
>> +        */
>> +       if (zhdr->first_chunks != 0 && zhdr->last_chunks == 0 &&
>> +           zhdr->start_middle - (zhdr->first_chunks + ZHDR_CHUNKS) >=
>> +                       BIG_CHUNK_GAP) {
>> +               mchunk_memmove(zhdr, zhdr->first_chunks + 1);
>> +               zhdr->start_middle = zhdr->first_chunks + 1;
>
> this should be first_chunks + ZHDR_CHUNKS, not + 1.
>
>> +               return 1;
>> +       } else if (zhdr->last_chunks != 0 && zhdr->first_chunks == 0 &&
>> +                  TOTAL_CHUNKS - (zhdr->last_chunks + zhdr->start_middle
>> +                                       + zhdr->middle_chunks) >=
>> +                       BIG_CHUNK_GAP) {
>> +               unsigned short new_start = NCHUNKS - zhdr->last_chunks -
>
> this should be TOTAL_CHUNKS, not NCHUNKS.

Right :/

>> +                       zhdr->middle_chunks;
>> +               mchunk_memmove(zhdr, new_start);
>> +               zhdr->start_middle = new_start;
>> +               return 1;
>> +       }
>> +
>> +       return 0;
>>  }
>>
>>  /**
>> --
>> 2.4.2