From: Tejun Heo <tj@kernel.org>
To: Boaz Harrosh <bharrosh@panasas.com>
Cc: Jan Kara <jack@suse.cz>, Jeff Moyer <jmoyer@redhat.com>,
Christoph Hellwig <hch@lst.de>,
jaxboe@fusionio.com, linux-kernel@vger.kernel.org,
linux-fsdevel@vger.kernel.org, linux-scsi@vger.kernel.org,
linux-ide@vger.kernel.org, linux-raid@vger.kernel.org,
James.Bottomley@suse.de, tytso@mit.edu, chris.mason@oracle.com,
swhiteho@redhat.com, konishi.ryusuke@lab.ntt.co.jp,
dm-devel@redhat.com, vst@vlnb.net, rwheeler@redhat.com,
hare@suse.de, neilb@suse.de, rusty@rustcorp.com.au,
mst@redhat.com, jeremy@goop.org, snitzer@redhat.com,
k-ueda@ct.jp.nec.com, Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH 26/30] ext4: do not send discards as barriers
Date: Tue, 31 Aug 2010 12:13:36 +0200 [thread overview]
Message-ID: <4C7CD5D0.40007@kernel.org> (raw)
In-Reply-To: <4C7CD47B.1050409@panasas.com>
Hello,
On 08/31/2010 12:07 PM, Boaz Harrosh wrote:
> I don't know all the specifics of the virtio driver and the KVM backend but
> don't the KVM target io is eventually directed to a local file or device?
> If so the scsi device has disappeard but the bulk of the data is in host cache
> at the backstore (file or bdev). Once all files are closed the data is synced
> to disk.
>
> Is it not the same as Ric's problem of disconnecting the sata cable but
> not dropping power to the drive. The main of the cache is still intact.
There are two layers of caching there.
drive cache - host page cache - guest
When guest issues FLUSH, qemu will translate it into fdatasync which
will flush the host page cache followed by FLUSH to the drive which
will flush the drive cache to the media. If you delete the host disk
device, it will be detached w/o host page cache flushed. So, although
it's not complete, it will lose good part of cache. With out write
out timeout increased and/or with laptop mode enabled, it will
probably lose most of cache.
Thanks.
--
tejun
next prev parent reply other threads:[~2010-08-31 10:13 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-08-25 15:47 [PATCHSET 2.6.36-rc2] block, fs: replace HARDBARRIER with FLUSH/FUA Tejun Heo
2010-08-25 15:47 ` [PATCH 01/30] ide: remove unnecessary blk_queue_flushing() test in do_ide_request() Tejun Heo
2010-08-25 15:47 ` [PATCH 02/30] block/loop: queue ordered mode should be DRAIN_FLUSH Tejun Heo
2010-08-25 15:47 ` [PATCH 03/30] block: kill QUEUE_ORDERED_BY_TAG Tejun Heo
2010-08-25 15:47 ` [PATCH 04/30] block: deprecate barrier and replace blk_queue_ordered() with blk_queue_flush() Tejun Heo
2010-08-30 15:37 ` Boaz Harrosh
2010-08-25 15:47 ` [PATCH 05/30] block: remove spurious uses of REQ_HARDBARRIER Tejun Heo
2010-08-25 15:47 ` [PATCH 06/30] block: misc cleanups in barrier code Tejun Heo
2010-08-25 15:47 ` [PATCH 07/30] block: drop barrier ordering by queue draining Tejun Heo
2010-08-25 15:47 ` [PATCH 08/30] block: rename blk-barrier.c to blk-flush.c Tejun Heo
2010-08-25 15:47 ` [PATCH 09/30] block: rename barrier/ordered to flush Tejun Heo
2010-08-25 15:47 ` [PATCH 10/30] block: implement REQ_FLUSH/FUA based interface for FLUSH/FUA requests Tejun Heo
2010-08-25 15:47 ` [PATCH 11/30] block: filter flush bio's in __generic_make_request() Tejun Heo
2010-08-25 15:47 ` [PATCH 12/30] block: use REQ_FLUSH in blkdev_issue_flush() Tejun Heo
2010-08-25 15:47 ` [PATCH 13/30] block: simplify queue_next_fseq Tejun Heo
2010-08-25 15:47 ` [PATCH 14/30] block/loop: implement REQ_FLUSH/FUA support Tejun Heo
2010-08-25 15:47 ` [PATCH 15/30] virtio_blk: drop REQ_HARDBARRIER support Tejun Heo
2010-08-25 15:47 ` [PATCH 16/30] lguest: replace VIRTIO_F_BARRIER support with VIRTIO_F_FLUSH support Tejun Heo
2010-08-25 15:47 ` [PATCH 17/30] md: implment REQ_FLUSH/FUA support Tejun Heo
2010-08-25 15:47 ` [PATCH 18/30] block: pass gfp_mask and flags to sb_issue_discard Tejun Heo
2010-08-25 15:47 ` [PATCH 19/30] xfs: replace barriers with explicit flush / FUA usage Tejun Heo
2010-08-25 15:47 ` [PATCH 20/30] btrfs: " Tejun Heo
2010-08-25 15:47 ` [PATCH 21/30] gfs2: " Tejun Heo
2010-08-25 15:47 ` [PATCH 22/30] reiserfs: " Tejun Heo
2010-08-25 15:47 ` [PATCH 23/30] nilfs2: " Tejun Heo
2010-08-25 15:47 ` [PATCH 24/30] jbd: " Tejun Heo
2010-08-25 15:47 ` [PATCH 25/30] jbd2: " Tejun Heo
2010-08-25 15:47 ` [PATCH 26/30] ext4: do not send discards as barriers Tejun Heo
2010-08-25 15:58 ` Christoph Hellwig
2010-08-25 16:00 ` Christoph Hellwig
2010-08-25 15:57 ` Tejun Heo
2010-08-25 20:02 ` Jan Kara
2010-08-26 8:25 ` Tejun Heo
2010-08-27 17:31 ` Jan Kara
2010-08-30 19:56 ` Jeff Moyer
2010-08-30 20:20 ` Jan Kara
2010-08-30 20:24 ` Ric Wheeler
2010-08-30 20:39 ` Vladislav Bolkhovitin
2010-08-30 21:02 ` Jan Kara
2010-08-31 9:55 ` Boaz Harrosh
2010-09-02 18:46 ` Vladislav Bolkhovitin
2010-08-30 21:01 ` Jeff Moyer
2010-08-31 8:11 ` Tejun Heo
2010-08-31 10:07 ` Boaz Harrosh
2010-08-31 10:13 ` Tejun Heo [this message]
2010-08-31 10:27 ` Boaz Harrosh
2010-09-09 22:53 ` Jan Kara
2010-08-25 15:47 ` [PATCH 27/30] fat: " Tejun Heo
2010-08-25 15:47 ` [PATCH 28/30] swap: " Tejun Heo
2010-08-25 15:47 ` [PATCH 29/30] block: remove the BLKDEV_IFL_BARRIER flag Tejun Heo
2010-08-25 15:59 ` Christoph Hellwig
2010-08-25 15:47 ` [PATCH 30/30] block: remove the BH_Eopnotsupp flag Tejun Heo
2010-08-25 16:03 ` [PATCHSET 2.6.36-rc2] block, fs: replace HARDBARRIER with FLUSH/FUA Mike Snitzer
2010-08-26 8:23 ` [PATCH 24.5/30] jbd2: Modify ASYNC_COMMIT code to not rely on queue draining on barrier Tejun Heo
2010-08-26 9:33 ` Sergei Shtylyov
2010-08-26 9:37 ` [PATCH UPDATED " Tejun Heo
2010-09-06 11:15 ` [PATCH " Andreas Dilger
2010-09-06 11:40 ` Jan Kara
2010-08-26 9:54 ` [PATCH] block: update documentation for REQ_FLUSH / REQ_FUA Christoph Hellwig
2010-08-27 9:18 ` Tejun Heo
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