linux-kernel - Re: [PATCH] btrfs: add block plug for .writepages

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Date:	Tue, 1 Nov 2011 14:31:38 +0900
From:	NamJae Jeon <linkinjeon@...il.com>
To:	Chris Mason <chris.mason@...cle.com>,
	Namjae Jeon <linkinjeon@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] btrfs: add block plug for .writepages

2011/11/1 Chris Mason <chris.mason@...cle.com>:
> On Tue, Nov 01, 2011 at 12:45:07AM +0900, Namjae Jeon wrote:
>> Add block plug for btrfs .writepages. Block plug is helpful to reduce block lock contention.
>>
>> Signed-off-by: Namjae Jeon <linkinjeon@...il.com>
>> ---
>>  fs/btrfs/extent_io.c |    4 ++++
>>  1 files changed, 4 insertions(+), 0 deletions(-)
>>
>> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
>> index d418164..8f2d6bd 100644
>> --- a/fs/btrfs/extent_io.c
>> +++ b/fs/btrfs/extent_io.c
>> @@ -2388,6 +2388,7 @@ static int extent_write_cache_pages(struct extent_io_tree *tree,
>>       pgoff_t end;            /* Inclusive */
>>       int scanned = 0;
>>       int tag;
>> +     struct blk_plug plug;
>>
>>       pagevec_init(&pvec, 0);
>>       if (wbc->range_cyclic) {
>> @@ -2405,6 +2406,8 @@ static int extent_write_cache_pages(struct extent_io_tree *tree,
>>  retry:
>>       if (wbc->sync_mode == WB_SYNC_ALL)
>>               tag_pages_for_writeback(mapping, index, end);
>> +
>> +     blk_start_plug(&plug);
>>       while (!done && !nr_to_write_done && (index <= end) &&
>>              (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
>>                       min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1))) {
>> @@ -2468,6 +2471,7 @@ retry:
>>               pagevec_release(&pvec);
>>               cond_resched();
>>       }
>> +     blk_finish_plug(&plug);
>>       if (!scanned && !done) {
>>               /*
>>                * We hit the last page and there is more work to be done: wrap
>
> Thanks for the patch, but we actually do this at a lower level in btrfs.
> The actual IO can be done to multiple block devices, so we try to plug
> for each device individually.
>
> -chris
>
>
Hi. Chris.

I got your point. pending bio is operated by worker_loop thread.
But Is block plug needed in extent_readpages ?

Thanks.
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