On Mon, Nov 28, 2016 at 9:14 AM, Vitaly Wool <vitalywool@xxxxxxxxx> wrote:
> On Fri, Nov 25, 2016 at 7:25 PM, Dan Streetman <ddstreet@xxxxxxxx> wrote:
>> On Tue, Nov 15, 2016 at 11:00 AM, Vitaly Wool <vitalywool@xxxxxxxxx> wrote:
>>> If a z3fold page couldn't be compacted, we don't want it to be
>>> used for next object allocation in the first place.
>>
>> why? !compacted can only mean 1) already compact or 2) middle chunks
>> is mapped. #1 is as good compaction-wise as the page can get, so do
>> you mean that if a page couldn't be compacted because of #2, we
>> shouldn't use it for next allocation? if so, that isn't quite what
>> this patch does.
>>
>>> It makes more
>>> sense to add it to the end of the relevant unbuddied list. If that
>>> page gets compacted later, it will be added to the beginning of
>>> the list then.
>>>
>>> This simple idea gives 5-7% improvement in randrw fio tests and
>>> about 10% improvement in fio sequential read/write.
>>
>> i don't understand why there is any improvement - the unbuddied lists
>> are grouped by the amount of free chunks, so all pages in a specific
>> unbuddied list should have exactly that number of free chunks
>> available, and it shouldn't matter if a page gets put into the front
>> or back...where is the performance improvement coming from?
>
> When the next attempt to compact this page comes, it's less likely
> it's locked so the wait times are slightly lower in average.
which wait time? for a page with the middle chunk mapped compact
should exit immediately...?
>
> ~vitaly
>
>>> Signed-off-by: Vitaly Wool <vitalywool@xxxxxxxxx>
>>> ---
>>> mm/z3fold.c | 22 +++++++++++++++++-----
>>> 1 file changed, 17 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/mm/z3fold.c b/mm/z3fold.c
>>> index ffd9353..e282ba0 100644
>>> --- a/mm/z3fold.c
>>> +++ b/mm/z3fold.c
>>> @@ -539,11 +539,19 @@ static void z3fold_free(struct z3fold_pool *pool, unsigned long handle)
>>> free_z3fold_page(zhdr);
>>> atomic64_dec(&pool->pages_nr);
>>> } else {
>>> - z3fold_compact_page(zhdr);
>>> + int compacted = z3fold_compact_page(zhdr);
>>> /* Add to the unbuddied list */
>>> spin_lock(&pool->lock);
>>> freechunks = num_free_chunks(zhdr);
>>> - list_add(&zhdr->buddy, &pool->unbuddied[freechunks]);
>>> + /*
>>> + * If the page has been compacted, we want to use it
>>> + * in the first place.
>>> + */
>>> + if (compacted)
>>> + list_add(&zhdr->buddy, &pool->unbuddied[freechunks]);
>>> + else
>>> + list_add_tail(&zhdr->buddy,
>>> + &pool->unbuddied[freechunks]);
>>> spin_unlock(&pool->lock);
>>> z3fold_page_unlock(zhdr);
>>> }
>>> @@ -672,12 +680,16 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
>>> spin_lock(&pool->lock);
>>> list_add(&zhdr->buddy, &pool->buddied);
>>> } else {
>>> - z3fold_compact_page(zhdr);
>>> + int compacted = z3fold_compact_page(zhdr);
>>> /* add to unbuddied list */
>>> spin_lock(&pool->lock);
>>> freechunks = num_free_chunks(zhdr);
>>> - list_add(&zhdr->buddy,
>>> - &pool->unbuddied[freechunks]);
>>> + if (compacted)
>>> + list_add(&zhdr->buddy,
>>> + &pool->unbuddied[freechunks]);
>>> + else
>>> + list_add_tail(&zhdr->buddy,
>>> + &pool->unbuddied[freechunks]);
>>> }
>>> }
>>>
>>> --
>>> 2.4.2
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