Messages in this thread | | | Date | Mon, 10 Apr 2006 13:45:32 +0200 (CEST) | From | Grzegorz Kulewski <> | Subject | Re: Slow swapon for big (12GB) swap |
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On Mon, 10 Apr 2006, Andrew Morton wrote: > Grzegorz Kulewski <kangur@polcom.net> wrote: >> On Mon, 10 Apr 2006, Andrew Morton wrote: >>> Grzegorz Kulewski <kangur@polcom.net> 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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