Messages in this thread | | | Date | Thu, 19 Jan 2012 20:58:39 -0500 (EST) | From | Mikulas Patocka <> | Subject | Re: [PATCH] block: Invalidate the cache for a parent block-device |
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Hi
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).
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.
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 >
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