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Message-Id: <1432881338-898-1-git-send-email-ming.lei@canonical.com>
Date: Fri, 29 May 2015 14:35:33 +0800
From: Ming Lei <ming.lei@...onical.com>
To: linux-kernel@...r.kernel.org,
Dave Kleikamp <dave.kleikamp@...cle.com>
Cc: Jens Axboe <axboe@...nel.dk>, Zach Brown <zab@...bo.net>,
Christoph Hellwig <hch@...radead.org>,
Maxim Patlasov <mpatlasov@...allels.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Alexander Viro <viro@...iv.linux.org.uk>,
Tejun Heo <tj@...nel.org>, Dave Chinner <david@...morbit.com>
Subject: [PATCH v4 0/4] block: loop: improve loop with AIO
Hi Guys,
There are about 3 advantages to use direct I/O and AIO on
read/write loop's backing file:
1) double cache can be avoided, then memory usage gets
decreased a lot
2) not like user space direct I/O, there isn't cost of
pinning pages
3) avoid context switch for obtaining good throughput
- in buffered file read, random I/O throughput is often obtained
only if they are submitted concurrently from lots of tasks; but for
sequential I/O, most of times they can be hit from page cache, so
concurrent submissions often introduce unnecessary context switch
and can't improve throughput much. There was such discussion[1]
to use non-blocking I/O to improve the problem for application.
- with direct I/O and AIO, concurrent submissions can be
avoided and random read throughput can't be affected meantime
So this patchset trys to improve loop via AIO, and about 45% memory
usage can be decreased, see detailed data in commit log of patch4,
also IO throughput isn't affected too.
V4:
- add detailed commit log for 'use kthread_work'
- allow userspace(sysfs, losetup) to decide if dio/aio is
used as suggested by Christoph and Dave Chinner
- only use dio if the backing block device's min io size
is 512 as pointed by Dave Chinner & Christoph
V3:
- based on Al's iov_iter work and Christoph's kiocb changes
- use kthread_work
- introduce IOCB_DONT_DIRTY_PAGE flag
- set QUEUE_FLAG_NOMERGES for loop's request queue
V2:
- remove 'extra' parameter to aio_kernel_alloc()
- try to avoid memory allcation inside queue req callback
- introduce 'use_mq' sysfs file for enabling kernel aio or disabling it
V1:
- link:
http://marc.info/?t=140803157700004&r=1&w=2
- improve failure path in aio_kernel_submit()
--
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