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Date: Tue, 22 Oct 2013 18:54:25 -0500 From: Alireza Haghdoost <alireza@...umn.edu> To: Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org Cc: Jerry Fredin <jerry.fredin@...app.com>, linux-aio@...ck.org, linux-fsdevel@...r.kernel.org Subject: [PATCH] block/aio: Enable sysfs nomerge control for I/O requests in the plug list This patch enables the sysfs to control I/O request merge functionality in the plug list. While this control has been implemented for the request queue, it was dismissed in the plug list. Therefore, block layer merges requests together (or attempt to merge) even if the merge capability was disable using sysfs nomerge parameter value 2. This limitation is directly affects functionality of io_submit() system call. The system call enables user to submit a bunch of IO requests from user space using struct iocb **ios input argument. However, the unconditioned merging functionality in the plug list potentially merges these requests together down the road. Therefore, there is no way to distinguish between an application sending bunch of sequential IOs and an application sending one big IO. Ultimately, all requests generated by the former app merge within the plug list together and looks similar to the second app. While the merging functionality is a desirable feature to improve the performance of IO subsystem for some applications, it is not useful for other application like ours at all. Signed-off-by: Alireza Haghdoost <alireza@...umn.edu> --- block/blk-core.c.orig 2013-10-22 15:26:59.484961156 -0500 +++ block/blk-core.c 2013-10-21 23:24:21.437887017 -0500 @@ -1420,7 +1420,7 @@ bool ret = false; plug = current->plug; - if (!plug) + if (!plug || blk_queue_nomerges(q) ) goto out; *request_count = 0; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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