On 12.12.18 г. 16:40 ч., David Sterba wrote:
> On Thu, Nov 29, 2018 at 06:41:31PM +0200, Nikolay Borisov wrote:
>> extent_readpages processes all pages in the readlist in batches of 16,
>> this is implemented by a single for loop but thanks to an if condition
>> the loop does 2 things based on whether we've filled the batch or not.
>> Additionally due to the structure of the code there is an additional
>> check which deals with partial batches.
>>
>> Streamline all of this by explicitly using two loops. The outter one is
>> used to process all pages while the inner one just fills in the batch
>> of 16 (currently). Due to this new structure the code guarantees that
>> all pages are processed in the loop hence the code to deal with any
>> leftovers is eliminated.
>>
>> This also enable the compiler to inline __extent_readpages:
>>
>> ./scripts/bloat-o-meter fs/btrfs/extent_io.o extent_io.for
>>
>> add/remove: 0/1 grow/shrink: 1/0 up/down: 660/-820 (-160)
>> Function old new delta
>> extent_readpages 476 1136 +660
>> __extent_readpages 820 - -820
>> Total: Before=44315, After=44155, chg -0.36%
>>
>> Signed-off-by: Nikolay Borisov <nbori...@suse.com>
>> ---
>> fs/btrfs/extent_io.c | 37 ++++++++++++++++---------------------
>> 1 file changed, 16 insertions(+), 21 deletions(-)
>>
>> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
>> index 8332c5f4b1c3..233f835dd6f8 100644
>> --- a/fs/btrfs/extent_io.c
>> +++ b/fs/btrfs/extent_io.c
>> @@ -4093,43 +4093,38 @@ int extent_writepages(struct address_space *mapping,
>> int extent_readpages(struct address_space *mapping, struct list_head *pages,
>> unsigned nr_pages)
>
> nr_pages becomes unused now. I've checked the MM code that calls here
> and it's guaranteed that the number of list 'pages' members is same as
> nr_pages.
Indeed, I missed that.
>
>> {
>> +#define BTRFS_PAGES_BATCH 16
>> +
>> struct bio *bio = NULL;
>> - unsigned page_idx;
>> unsigned long bio_flags = 0;
>> - struct page *pagepool[16];
>> - struct page *page;
>> + struct page *pagepool[BTRFS_PAGES_BATCH];
>
> I don't think we need the extra define, if
>
> struct page *pagepool[16];
>
> ...
>
> for (nr = 0; nr < ARRAY_SIZE(pagepool) ...
>
> Otherwise ok, nice cleanup.
Fair enough, I'm ok with that as well.
>
> Reviewed-by: David Sterba <dste...@suse.com>
>
