On Mon, 10 Apr 2006, Andrew Morton wrote:
Grzegorz Kulewski <[email protected]> wrote:
On Mon, 10 Apr 2006, Andrew Morton wrote:
Grzegorz Kulewski <[email protected]> wrote:
I am using big swap here (as a backing for potentially huge tmpfs). And I
wonder why swapon on such big (like 12GB) swap takes about 7 minutes
(continuous disk IO).
It's a bit quicker here:
vmm:/usr/src/25# mkswap /dev/hda6
Setting up swapspace version 1, size = 54031826 kB
vmm:/usr/src/25# time swapon /dev/hda6
swapon /dev/hda6 0.00s user 0.04s system 74% cpu 0.054 total
Is this expected?
Nope.
Why it is like that?
Are you using a swapfile or a swap partition?
Swap file.
If it's a swapfile then perhaps the filesystem is being inefficient in its
bmap() function. Which filesystem is it?
Ext3.
OK. A 12G file is around 3000 indirect blocks. At 10 milliseconds each
I'd expect it to take 30-odd seconds. A 14G swapfile here takes 20 second
for swapon.
That is what I would expect.
Maybe your disks are slow, or the fs is already quite full+fragmented.
Well, the disk is slow but not that slow... For example dd creating this
file goes at about 20-25MB/s and takes about 10 minutes IIRC, so it is not
*that* bad...
The disk is not full or even close to:
/dev/hda4 /mnt/data 52552,1 27343,6 24140,4 54% ext3
and file count is not that high too:
/dev/hda4 6836224 42333 6793891 1% /mnt/data
and it should not be fragmented in any way. It is rather new (3 months
old) filesystem with several bigger files and small amount of smaller.
Used mainly as a data store and backup. Very infrequently written to (new
blocks/files).
I think I will test new kernel soon. Maybe with and without -ck. Maybe
disk scheduler (probably CFQ) does something stupid... Or swap prefetch...
Or anything...
Thanks,
Grzegorz Kulewski
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