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

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
...@@ -38,28 +38,29 @@ void blk_recalc_rq_sectors(struct request *rq, int nsect) ...@@ -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) ...@@ -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);
......
...@@ -708,6 +708,8 @@ struct req_iterator { ...@@ -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)
......
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