Messages in this thread | | | From | Ming Lei <> | Subject | [PATCH v4 0/4] block: loop: improve loop with AIO | Date | Fri, 29 May 2015 14:35:33 +0800 |
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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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