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vfs: make guard_bh_eod() more generic 

This patchset implements readpages() operation for block device by using
mpage_readpages() which can create multipage BIOs instead of BIOs for each
page and reduce system CPU time consumption.

This patch (of 3):

guard_bh_eod() is used in submit_bh() to allow us to do IO even on the odd
last sectors of a device, even if the block size is some multiple of the
physical sector size.  This makes guard_bh_eod() more generic and renames
it guard_bio_eod() so that we can use it without struct buffer_head
argument.

The reason for this change is that using mpage_readpages() for block
device requires to add this guard check in mpage code.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Akinobu Mita 2014-10-09 15:26:53 -07:00 committed by Linus Torvalds
parent 21bb9bd194
commit 59d43914ed
1 changed files with 12 additions and 14 deletions
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26
fs/buffer.c
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@ -2956,7 +2956,7 @@ static void end_bio_bh_io_sync(struct bio *bio, int err)
/*
* This allows us to do IO even on the odd last sectors
* of a device, even if the bh block size is some multiple
* of a device, even if the block size is some multiple
* of the physical sector size.
*
* We'll just truncate the bio to the size of the device,
@ -2966,10 +2966,11 @@ static void end_bio_bh_io_sync(struct bio *bio, int err)
* errors, this only handles the "we need to be able to
* do IO at the final sector" case.
*/
static void guard_bh_eod(int rw, struct bio *bio, struct buffer_head *bh)
static void guard_bio_eod(int rw, struct bio *bio)
{
sector_t maxsector;
unsigned bytes;
struct bio_vec *bvec = &bio->bi_io_vec[bio->bi_vcnt - 1];
unsigned truncated_bytes;
maxsector = i_size_read(bio->bi_bdev->bd_inode) >> 9;
if (!maxsector)
@ -2984,23 +2985,20 @@ static void guard_bh_eod(int rw, struct bio *bio, struct buffer_head *bh)
return;
maxsector -= bio->bi_iter.bi_sector;
bytes = bio->bi_iter.bi_size;
if (likely((bytes >> 9) <= maxsector))
if (likely((bio->bi_iter.bi_size >> 9) <= maxsector))
return;
/* Uhhuh. We've got a bh that straddles the device size! */
bytes = maxsector << 9;
/* Uhhuh. We've got a bio that straddles the device size! */
truncated_bytes = bio->bi_iter.bi_size - (maxsector << 9);
/* Truncate the bio.. */
bio->bi_iter.bi_size = bytes;
bio->bi_io_vec[0].bv_len = bytes;
bio->bi_iter.bi_size -= truncated_bytes;
bvec->bv_len -= truncated_bytes;
/* ..and clear the end of the buffer for reads */
if ((rw & RW_MASK) == READ) {
void *kaddr = kmap_atomic(bh->b_page);
memset(kaddr + bh_offset(bh) + bytes, 0, bh->b_size - bytes);
kunmap_atomic(kaddr);
flush_dcache_page(bh->b_page);
zero_user(bvec->bv_page, bvec->bv_offset + bvec->bv_len,
truncated_bytes);
}
}
@ -3041,7 +3039,7 @@ int _submit_bh(int rw, struct buffer_head *bh, unsigned long bio_flags)
bio->bi_flags |= bio_flags;
/* Take care of bh's that straddle the end of the device */
guard_bh_eod(rw, bio, bh);
guard_bio_eod(rw, bio);
if (buffer_meta(bh))
rw |= REQ_META;