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: Jens Axboe <jens.axboe@oracle.com>
2 files changed