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Commit 59d43914 authored by Akinobu Mita's avatar Akinobu Mita Committed by Linus Torvalds
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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: default avatarAkinobu 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 21bb9bd1

fs/buffer.c

+12 −14
Original line number Original line Diff line number Diff line
@@ -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

 * 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.

 * of the physical sector size.

 *

 *

 * We'll just truncate the bio to the size of the device,

 * 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

 * errors, this only handles the "we need to be able to

 * do IO at the final sector" case.

 * 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;

	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;

	maxsector = i_size_read(bio->bi_bdev->bd_inode) >> 9;

	if (!maxsector)

	if (!maxsector)
@@ -2984,23 +2985,20 @@ static void guard_bh_eod(int rw, struct bio *bio, struct buffer_head *bh) 
		return;

		return;





	maxsector -= bio->bi_iter.bi_sector;

	maxsector -= bio->bi_iter.bi_sector;

	bytes = bio->bi_iter.bi_size;

	if (likely((bio->bi_iter.bi_size >> 9) <= maxsector))

	if (likely((bytes >> 9) <= maxsector))

		return;

		return;





	/* Uhhuh. We've got a bh that straddles the device size! */

	/* Uhhuh. We've got a bio that straddles the device size! */

	bytes = maxsector << 9;

	truncated_bytes = bio->bi_iter.bi_size - (maxsector << 9);





	/* Truncate the bio.. */

	/* Truncate the bio.. */

	bio->bi_iter.bi_size = bytes;

	bio->bi_iter.bi_size -= truncated_bytes;

	bio->bi_io_vec[0].bv_len = bytes;

	bvec->bv_len -= truncated_bytes;





	/* ..and clear the end of the buffer for reads */

	/* ..and clear the end of the buffer for reads */

	if ((rw & RW_MASK) == READ) {

	if ((rw & RW_MASK) == READ) {

		void *kaddr = kmap_atomic(bh->b_page);

		zero_user(bvec->bv_page, bvec->bv_offset + bvec->bv_len,

		memset(kaddr + bh_offset(bh) + bytes, 0, bh->b_size - bytes);

				truncated_bytes);

		kunmap_atomic(kaddr);

		flush_dcache_page(bh->b_page);

	}

	}

}

}
@@ -3041,7 +3039,7 @@ int _submit_bh(int rw, struct buffer_head *bh, unsigned long bio_flags) 
	bio->bi_flags |= bio_flags;

	bio->bi_flags |= bio_flags;





	/* Take care of bh's that straddle the end of the device */

	/* 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))

	if (buffer_meta(bh))

		rw |= REQ_META;

		rw |= REQ_META;