From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:36491) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YGXWo-000076-5r for qemu-devel@nongnu.org; Wed, 28 Jan 2015 13:39:50 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1YGXWi-0008Qo-R1 for qemu-devel@nongnu.org; Wed, 28 Jan 2015 13:39:50 -0500 Received: from mailhub.sw.ru ([195.214.232.25]:22547 helo=relay.sw.ru) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YGXWi-0008KV-F0 for qemu-devel@nongnu.org; Wed, 28 Jan 2015 13:39:44 -0500 From: "Denis V. Lunev" Date: Wed, 28 Jan 2015 21:38:56 +0300 Message-Id: <1422470338-20465-6-git-send-email-den@openvz.org> In-Reply-To: <1422470338-20465-1-git-send-email-den@openvz.org> References: <1422470338-20465-1-git-send-email-den@openvz.org> Subject: [Qemu-devel] [PATCH 5/7] block: use fallocate(FALLOC_FL_PUNCH_HOLE) & fallocate(0) to write zeroes List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , Fam Zheng , Peter Lieven , qemu-devel@nongnu.org, Max Reitz , Stefan Hajnoczi , "Denis V. Lunev" This sequence works efficiently if FALLOC_FL_ZERO_RANGE is not supported. Unfortunately, FALLOC_FL_ZERO_RANGE is supported on really modern systems and only for a couple of filesystems. FALLOC_FL_PUNCH_HOLE is much more mature. The sequence of 2 operations FALLOC_FL_PUNCH_HOLE and 0 is necessary due to the following reasons: - FALLOC_FL_PUNCH_HOLE creates a hole in the file, the file becomes sparse. In order to retain original functionality we must allocate disk space afterwards. This is done using fallocate(0) call - fallocate(0) without preceeding FALLOC_FL_PUNCH_HOLE will do nothing if called above already allocated areas of the file, i.e. the content will not be zeroed This should increase the performance a bit for not-so-modern kernels. Signed-off-by: Denis V. Lunev CC: Max Reitz CC: Kevin Wolf CC: Stefan Hajnoczi CC: Peter Lieven CC: Fam Zheng --- block/raw-posix.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/block/raw-posix.c b/block/raw-posix.c index 5a777e7..2e24829 100644 --- a/block/raw-posix.c +++ b/block/raw-posix.c @@ -965,6 +965,21 @@ static ssize_t handle_aiocb_write_zeroes(RawPosixAIOData *aiocb) } #endif +#ifdef CONFIG_FALLOCATE_PUNCH_HOLE + if (s->has_discard) { + int ret = do_fallocate(s->fd, + FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, + aiocb->aio_offset, aiocb->aio_nbytes); + if (ret == 0) { + ret = do_fallocate(s->fd, 0, aiocb->aio_offset, aiocb->aio_nbytes); + } + if (ret != -ENOTSUP) { + return ret; + } + s->has_discard = false; + } +#endif + return -ENOTSUP; } -- 1.9.1