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Commit 1e428079 authored by Jens Axboe's avatar Jens Axboe
Browse files

block: reduce stack footprint of blk_recount_segments() 



blk_recalc_rq_segments() requires a request structure passed in, which
we don't have from blk_recount_segments(). So the latter allocates one on
the stack, using > 400 bytes of stack for that. This can cause us to spill
over one page of stack from ext4 at least:

 0)     4560     400   blk_recount_segments+0x43/0x62
 1)     4160      32   bio_phys_segments+0x1c/0x24
 2)     4128      32   blk_rq_bio_prep+0x2a/0xf9
 3)     4096      32   init_request_from_bio+0xf9/0xfe
 4)     4064     112   __make_request+0x33c/0x3f6
 5)     3952     144   generic_make_request+0x2d1/0x321
 6)     3808      64   submit_bio+0xb9/0xc3
 7)     3744      48   submit_bh+0xea/0x10e
 8)     3696     368   ext4_mb_init_cache+0x257/0xa6a [ext4]
 9)     3328     288   ext4_mb_regular_allocator+0x421/0xcd9 [ext4]
10)     3040     160   ext4_mb_new_blocks+0x211/0x4b4 [ext4]
11)     2880     336   ext4_ext_get_blocks+0xb61/0xd45 [ext4]
12)     2544      96   ext4_get_blocks_wrap+0xf2/0x200 [ext4]
13)     2448      80   ext4_da_get_block_write+0x6e/0x16b [ext4]
14)     2368     352   mpage_da_map_blocks+0x7e/0x4b3 [ext4]
15)     2016     352   ext4_da_writepages+0x2ce/0x43c [ext4]
16)     1664      32   do_writepages+0x2d/0x3c
17)     1632     144   __writeback_single_inode+0x162/0x2cd
18)     1488      96   generic_sync_sb_inodes+0x1e3/0x32b
19)     1392      16   sync_sb_inodes+0xe/0x10
20)     1376      48   writeback_inodes+0x69/0xb3
21)     1328     208   balance_dirty_pages_ratelimited_nr+0x187/0x2f9
22)     1120     224   generic_file_buffered_write+0x1d4/0x2c4
23)      896     176   __generic_file_aio_write_nolock+0x35f/0x393
24)      720      80   generic_file_aio_write+0x6c/0xc8
25)      640      80   ext4_file_write+0xa9/0x137 [ext4]
26)      560     320   do_sync_write+0xf0/0x137
27)      240      48   vfs_write+0xb3/0x13c
28)      192      64   sys_write+0x4c/0x74
29)      128     128   system_call_fastpath+0x16/0x1b

Split the segment counting out into a __blk_recalc_rq_segments() helper
to avoid allocating an onstack request just for checking the physical
segment count.

Signed-off-by: default avatarJens Axboe <jens.axboe@oracle.com>
parent 5e4c91c8

block/blk-merge.c

+53 −41
Original line number Original line Diff line number Diff line
@@ -38,28 +38,29 @@ void blk_recalc_rq_sectors(struct request *rq, int nsect) 
	}

	}

}

}





void blk_recalc_rq_segments(struct request *rq)

static unsigned int __blk_recalc_rq_segments(struct request_queue *q,

					     struct bio *bio,

					     unsigned int *seg_size_ptr)

{

{

	int nr_phys_segs;

	unsigned int phys_size;

	unsigned int phys_size;

	struct bio_vec *bv, *bvprv = NULL;

	struct bio_vec *bv, *bvprv = NULL;

	int seg_size;

	int cluster, i, high, highprv = 1;

	int cluster;

	unsigned int seg_size, nr_phys_segs;

	struct req_iterator iter;

	struct bio *fbio;

	int high, highprv = 1;

	struct request_queue *q = rq->q;





	if (!rq->bio)

	if (!bio)

		return;

		return 0;





	fbio = bio;

	cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);

	cluster = test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);

	seg_size = 0;

	seg_size = 0;

	phys_size = nr_phys_segs = 0;

	phys_size = nr_phys_segs = 0;

	rq_for_each_segment(bv, rq, iter) {

	for_each_bio(bio) {

		bio_for_each_segment(bv, bio, i) {

			/*

			/*

		 * the trick here is making sure that a high page is never

			 * the trick here is making sure that a high page is

		 * considered part of another segment, since that might

			 * never considered part of another segment, since that

		 * change with the bounce page.

			 * might change with the bounce page.

			 */

			 */

			high = page_to_pfn(bv->bv_page) > q->bounce_pfn;

			high = page_to_pfn(bv->bv_page) > q->bounce_pfn;

			if (high || highprv)

			if (high || highprv)
@@ -77,33 +78,44 @@ void blk_recalc_rq_segments(struct request *rq) 
				continue;

				continue;

			}

			}

new_segment:

new_segment:

		if (nr_phys_segs == 1 && seg_size > rq->bio->bi_seg_front_size)

			if (nr_phys_segs == 1 && seg_size >

			rq->bio->bi_seg_front_size = seg_size;

			    fbio->bi_seg_front_size)

				fbio->bi_seg_front_size = seg_size;





			nr_phys_segs++;

			nr_phys_segs++;

			bvprv = bv;

			bvprv = bv;

			seg_size = bv->bv_len;

			seg_size = bv->bv_len;

			highprv = high;

			highprv = high;

		}

		}

	}



	if (seg_size_ptr)

		*seg_size_ptr = seg_size;





	if (nr_phys_segs == 1 && seg_size > rq->bio->bi_seg_front_size)

	return nr_phys_segs;

}



void blk_recalc_rq_segments(struct request *rq)

{

	unsigned int seg_size = 0, phys_segs;



	phys_segs = __blk_recalc_rq_segments(rq->q, rq->bio, &seg_size);



	if (phys_segs == 1 && seg_size > rq->bio->bi_seg_front_size)

		rq->bio->bi_seg_front_size = seg_size;

		rq->bio->bi_seg_front_size = seg_size;

	if (seg_size > rq->biotail->bi_seg_back_size)

	if (seg_size > rq->biotail->bi_seg_back_size)

		rq->biotail->bi_seg_back_size = seg_size;

		rq->biotail->bi_seg_back_size = seg_size;





	rq->nr_phys_segments = nr_phys_segs;

	rq->nr_phys_segments = phys_segs;

}

}





void blk_recount_segments(struct request_queue *q, struct bio *bio)

void blk_recount_segments(struct request_queue *q, struct bio *bio)

{

{

	struct request rq;

	struct bio *nxt = bio->bi_next;

	struct bio *nxt = bio->bi_next;

	rq.q = q;



	rq.bio = rq.biotail = bio;

	bio->bi_next = NULL;

	bio->bi_next = NULL;

	blk_recalc_rq_segments(&rq);

	bio->bi_phys_segments = __blk_recalc_rq_segments(q, bio, NULL);

	bio->bi_next = nxt;

	bio->bi_next = nxt;

	bio->bi_phys_segments = rq.nr_phys_segments;

	bio->bi_flags |= (1 << BIO_SEG_VALID);

	bio->bi_flags |= (1 << BIO_SEG_VALID);

}

}

EXPORT_SYMBOL(blk_recount_segments);

EXPORT_SYMBOL(blk_recount_segments);

include/linux/blkdev.h

+2 −0
Original line number Original line Diff line number Diff line
@@ -708,6 +708,8 @@ struct req_iterator { 
};

};





/* This should not be used directly - use rq_for_each_segment */

/* This should not be used directly - use rq_for_each_segment */

#define for_each_bio(_bio)		\

	for (; _bio; _bio = _bio->bi_next)

#define __rq_for_each_bio(_bio, rq)	\

#define __rq_for_each_bio(_bio, rq)	\

	if ((rq->bio))			\

	if ((rq->bio))			\

		for (_bio = (rq)->bio; _bio; _bio = _bio->bi_next)

		for (_bio = (rq)->bio; _bio; _bio = _bio->bi_next)