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

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Date:	Tue, 1 Nov 2011 21:26:40 +0900
From:	NamJae Jeon <linkinjeon@...il.com>
To:	Shaohua Li <shaohua.li@...el.com>
Cc:	Chris Mason <chris.mason@...cle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] btrfs: add block plug for .writepages

2011/11/1 Shaohua Li <shaohua.li@...el.com>:
> 2011/11/1 NamJae Jeon <linkinjeon@...il.com>:
>> 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 ?
> .readpages are called in readahead, where we already have block
> plug.
Thanks for your reply. I checked it.
block plug in mpage_readpages is not needed also.
>
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