From mboxrd@z Thu Jan 1 00:00:00 1970 From: Josef Bacik Subject: Re: [PATCH 3/4] btrfs: don't spin in shrink_delalloc if there is nothing to free Date: Mon, 09 May 2011 12:00:28 -0400 Message-ID: <4DC80F9C.10706@redhat.com> References: <1304803784-23756-1-git-send-email-slyfox@gentoo.org> <1304803784-23756-2-git-send-email-slyfox@gentoo.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Cc: linux-btrfs@vger.kernel.org, Chris Mason , Sergei Trofimovich To: slyich@gmail.com Return-path: In-Reply-To: <1304803784-23756-2-git-send-email-slyfox@gentoo.org> List-ID: On 05/07/2011 05:29 PM, slyich@gmail.com wrote: > Observed as a large delay when --mixed filesystem is filled up. > Test example: > 1. create tiny --mixed FS: > $ dd if=/dev/zero of=2G.img seek=$((2048 * 1024 * 1024 - 1)) count=1 bs=1 > $ mkfs.btrfs --mixed 2G.img > $ mount -oloop 2G.img /mnt/ut/ > 2. Try to fill it up: > $ dd if=/dev/urandom of=10M.file bs=10240 count=1024 > $ seq 1 256 | while read file_no; do echo $file_no; time cp 10M.file ${file_no}.copy; done > > Up to '200.copy' it goes fast, but when disk fills-up each -ENOSPC > message takes 3 seconds to pop-up _every_ ENOSPC (and in usermode linux > it's even more: 30-60 seconds!). (Maybe, time depends on kernel's timer resolution). > > No IO, no CPU load, just rescheduling. Some debugging revealed busy spinning > in shrink_delalloc. > > Signed-off-by: Sergei Trofimovich > --- > fs/btrfs/extent-tree.c | 4 ++++ > 1 files changed, 4 insertions(+), 0 deletions(-) > > diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c > index 9ee6bd5..9f5fdd3 100644 > --- a/fs/btrfs/extent-tree.c > +++ b/fs/btrfs/extent-tree.c > @@ -3425,6 +3425,10 @@ static int shrink_delalloc(struct btrfs_trans_handle *trans, > if (reserved == 0) > return 0; > > + /* nothing to shrink - nothing to reclaim */ > + if (root->fs_info->delalloc_bytes == 0) > + return 0; > + > max_reclaim = min(reserved, to_reclaim); > > while (loops< 1024) { Nice catch, you can add Reviewed-by: Josef Bacik Thanks, Josef