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SubjectRe: [PATCH] xfs: use smaller int param in call to xfs_flush_pages
On Mon, Apr 21, 2008 at 10:18:24PM -0500, Eric Sandeen wrote:
> FWIW this one also seems to make no stack difference, at least on x86_64.
>
> Not complaining; just checking it out. :)
>
> If you can shink xfs_bmapi, let me know. :)

FWIW, the path we care about is this path through ->writepage:

(submit_bio)
_xfs_buf_ioapply 32
xfs_buf_iorequest 0
xfs_buf_iostart 0
xfs_buf_read_flags 0
xfs_trans_read_buf 4
xfs_btree_read_bufs 16
xfs_alloc_lookup 56
xfs_alloc_lookup_eq 16
xfs_alloc_fixup_trees 20
xfs_alloc_ag_vextent_near 76
xfs_alloc_ag_vextent 0
xfs_alloc_vextent 48
xfs_bmap_btalloc 164
xfs_bmap_alloc 0
xfs_bmapi 228
xfs_iomap_write_allocate 116
xfs_iomap 20
xfs_map_blocks 16
xfs_page_state_convert 124
xfs_vm_writepage 12
-------------------------------------
checkstack total: 948
Realistically, the onyl thing we can trim anything off is xfs_bmapi,
xfs_bmap_btalloc, xfs_iomap_write_allocate, and xfs_page_state_convert.
It's going to take a lot of work to get any significant change into
those functions given the complexity of them....
FWIW, if we've come through a syscall, the rest of the trace looks
like:

__writepage 0
write_cache_pages 100
generic_writepages 0
xfs_vm_writepages 12
do_writepages 0
__writeback_single_inode 36
sync_sb_inodes 40
writeback_inodes 0
balance_dirty_pages_ratelimited_nr 76
generic_file_buffered_write 96
xfs_write 80
xfs_file_aio_write 12
do_sync_write 140
vfs_write 12
--------------------------------------------
total 604
So the normal case uses 604 bytes prior to entering ->writepage.

It's when we are already using >2k of the stack when we enter
->writepage that we get into trouble....
Cheers,

Dave.
--
Dave Chinner
Principal Engineer
SGI Australian Software Group


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