Messages in this thread | | | Date | Fri, 20 Jan 2012 09:35:42 +0000 | From | Niels de Vos <> | Subject | Re: [PATCH] block: Invalidate the cache for a parent block-device |
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On 01/20/2012 01:58 AM, Mikulas Patocka wrote: > This definitely doesn't belong to blkdev_issue_flush. > > blkdev_issue_flush is called by filesystems each time they want to > synchronize hardware disk cache (for example, when committing a journal).
Ay, that sounds bad.
> The patch may cause serious performance regressions (each time a > filesystem commits journal, the patch causes it to walk all buffers in the > whole-disk device). > > You should put this code into fsync_bdev (so that it is called only on > fsync or BLKFLSBUF) and not to blkdev_issue_flush.
Hmm, I actually thought about that earlier, but decided that blkdev_issue_flush() was nicer. Looking at it again, I'm not sure why I thought that.
I'll post a 2nd version soon.
Thanks, Niels
> Mikulas > >> Executing a BLKFLSBUF-ioctl on a partition flushes the caches for that >> partition but reading data through the parent device will still return >> the old cached data. >> >> The cache for the block-device is not synced if the block-device is kept >> open (due to a mounted partition, for example). Only when all users for >> the disk have exited, the cache for the disk is made consistent again. >> >> Calling invalidate_bdev() on the parent block-device in case >> blkdev_issue_flush() was called for a partition fixes this. >> >> The problem can be worked around by forcing the caches to be flushed >> with either >> # blockdev --flushbufs ${dev_disk} >> or >> # echo 3 > /proc/sys/vm/drop_caches >> >> CC: Bryn M. Reeves <bmr <at> redhat.com> >> Signed-off-by: Niels de Vos <ndevos <at> redhat.com> >> --- >> block/blk-flush.c | 3 +++ >> 1 files changed, 3 insertions(+), 0 deletions(-) >> >> diff --git a/block/blk-flush.c b/block/blk-flush.c >> index 720ad60..e876f8e 100644 >> --- a/block/blk-flush.c >> +++ b/block/blk-flush.c >> @@ -448,6 +448,9 @@ int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_ >> >> if (!bio_flagged(bio, BIO_UPTODATE)) >> ret = -EIO; >> + else if (bdev != bdev->bd_contains) >> + /* invalidate parent block_device */ >> + invalidate_bdev(bdev->bd_contains); >> >> bio_put(bio); >> return ret; >> -- >> 1.7.6.5 >>
-- Niels de Vos Software Maintenance Engineer Support Engineering Group Red Hat UK, Ltd.
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