linux-kernel - Re: [PATCH 07/10] fs: make generic file read/write functions plug

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Message-ID: <4D70E78D.9000402@fusionio.com>
Date:	Fri, 4 Mar 2011 14:22:21 +0100
From:	Jens Axboe <jaxboe@...ionio.com>
To:	Vivek Goyal <vgoyal@...hat.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"hch@...radead.org" <hch@...radead.org>
Subject: Re: [PATCH 07/10] fs: make generic file read/write functions plug

On 2011-03-04 05:09, Vivek Goyal wrote:
> On Sat, Jan 22, 2011 at 01:17:26AM +0000, Jens Axboe wrote:
>> Signed-off-by: Jens Axboe <jaxboe@...ionio.com>
>> ---
>>  mm/filemap.c |    7 +++++++
>>  1 files changed, 7 insertions(+), 0 deletions(-)
>>
>> diff --git a/mm/filemap.c b/mm/filemap.c
>> index 380776c..f9a29c8 100644
>> --- a/mm/filemap.c
>> +++ b/mm/filemap.c
>> @@ -1243,12 +1243,15 @@ generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
>>  	unsigned long seg = 0;
>>  	size_t count;
>>  	loff_t *ppos = &iocb->ki_pos;
>> +	struct blk_plug plug;
>>  
>>  	count = 0;
>>  	retval = generic_segment_checks(iov, &nr_segs, &count, VERIFY_WRITE);
>>  	if (retval)
>>  		return retval;
>>  
>> +	blk_start_plug(&plug);
>> +
> 
> Jens,
> 
> IIUC, read requests will be considered SYNC and it looks like that
> __make_request() will dispatch all the SYNC requests immediately. If
> that's the case then for read path blk_plug mechanism is not required?

Good catch, we need to modify that logic. If the task is currently
plugged, it should not dispatch until blk_finish_plug() is called.
Essentially SYNC will not control dispatch. Will allow us to clean up
that logic, too.

-- 
Jens Axboe

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