Revision c4f675cd40d955d539180506c09515c90169b15b authored by Sergei Trofimovich on 20 May 2011, 20:20:30 UTC, committed by Chris Mason on 23 May 2011, 17:24:14 UTC
Observed as a large delay when --mixed filesystem is filled up.
Test example:
1. create tiny --mixed FS:
$ dd if=/dev/zero of=2G.img seek=$((2048 * 1024 * 1024 - 1)) count=1 bs=1
$ mkfs.btrfs --mixed 2G.img
$ mount -oloop 2G.img /mnt/ut/
2. Try to fill it up:
$ dd if=/dev/urandom of=10M.file bs=10240 count=1024
$ seq 1 256 | while read file_no; do echo $file_no; time cp 10M.file ${file_no}.copy; done
Up to '200.copy' it goes fast, but when disk fills-up each -ENOSPC
message takes 3 seconds to pop-up _every_ ENOSPC (and in usermode linux
it's even more: 30-60 seconds!). (Maybe, time depends on kernel's timer resolution).
No IO, no CPU load, just rescheduling. Some debugging revealed busy spinning
in shrink_delalloc.
Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
Reviewed-by: Josef Bacik <josef@redhat.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
1 parent 0f3b708
strncpy.S
/*
* arch/alpha/lib/strncpy.S
* Contributed by Richard Henderson (rth@tamu.edu)
*
* Copy no more than COUNT bytes of the null-terminated string from
* SRC to DST. If SRC does not cover all of COUNT, the balance is
* zeroed.
*
* Or, rather, if the kernel cared about that weird ANSI quirk. This
* version has cropped that bit o' nastiness as well as assuming that
* __stxncpy is in range of a branch.
*/
.set noat
.set noreorder
.text
.align 4
.globl strncpy
.ent strncpy
strncpy:
.frame $30, 0, $26
.prologue 0
mov $16, $0 # set return value now
beq $18, $zerolen
unop
bsr $23, __stxncpy # do the work of the copy
unop
bne $18, $multiword # do we have full words left?
subq $24, 1, $3 # nope
subq $27, 1, $4
or $3, $24, $3 # clear the bits between the last
or $4, $27, $4 # written byte and the last byte in COUNT
andnot $3, $4, $4
zap $1, $4, $1
stq_u $1, 0($16)
ret
.align 4
$multiword:
subq $27, 1, $2 # clear the final bits in the prev word
or $2, $27, $2
zapnot $1, $2, $1
subq $18, 1, $18
stq_u $1, 0($16)
addq $16, 8, $16
unop
beq $18, 1f
nop
unop
nop
blbc $18, 0f
stq_u $31, 0($16) # zero one word
subq $18, 1, $18
addq $16, 8, $16
beq $18, 1f
0: stq_u $31, 0($16) # zero two words
subq $18, 2, $18
stq_u $31, 8($16)
addq $16, 16, $16
bne $18, 0b
1: ldq_u $1, 0($16) # clear the leading bits in the final word
subq $24, 1, $2
or $2, $24, $2
zap $1, $2, $1
stq_u $1, 0($16)
$zerolen:
ret
.end strncpy
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