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dma Guru
Joined: 31 Jan 2003 Posts: 437 Location: Charlotte, NC, USA
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Posted: Thu Jun 12, 2003 12:27 am Post subject: kswapd reaching 97% CPU utilization under heavy disk IO. |
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(EDIT: I'm in UDMA5 mode in case you miss it in there...)
In one terminal, I did this:
Code: | dd if=/dev/zero of=/crap bs=8k count=20000 |
top gives me this:
Code: | PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ Command
4 root 25 0 0 0 0 R 97.3 0.0 178:13.52 kswapd
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The machine DOES get VERY unresponsive.
here's some output from hdparm:
Code: | root@laureate:~# hdparm -i /dev/hda
/dev/hda:
Model=Maxtor 54098H8, FwRev=DAC10SC0, SerialNo=K80BNJFC
Config={ Fixed }
RawCHS=16383/16/63, TrkSize=0, SectSize=0, ECCbytes=57
BuffType=DualPortCache, BuffSize=2048kB, MaxMultSect=16, MultSect=16
CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=80041248
IORDY=on/off, tPIO={min:120,w/IORDY:120}, tDMA={min:120,rec:120}
PIO modes: pio0 pio1 pio2 pio3 pio4
DMA modes: mdma0 mdma1 mdma2
UDMA modes: udma0 udma1 udma2 udma3 udma4 *udma5
AdvancedPM=yes: disabled (255) WriteCache=enabled
Drive conforms to: ATA/ATAPI-6 T13 1410D revision 0: 1 2 3 4 5 6
root@laureate:~# hdparm -tT /dev/hda
/dev/hda:
Timing buffer-cache reads: 128 MB in 0.42 seconds =301.89 MB/sec
Timing buffered disk reads: 64 MB in 2.26 seconds = 28.28 MB/sec
root@laureate:~#
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For the record, I'm using an A7V8X board with this:
Code: | 00:11.0 ISA bridge: VIA Technologies, Inc. VT8235 ISA Bridge
00:11.1 IDE interface: VIA Technologies, Inc. VT82C586/B/686A/B PIPC Bus Master IDE (rev 06) |
Here's some output from free:
Before dd:
Code: | root@laureate:~# free
total used free shared buffers cached
Mem: 773220 607884 165336 0 150080 337120
-/+ buffers/cache: 120684 652536
Swap: 2000084 8040 1992044 |
During dd:
Code: | root@laureate:~# free
total used free shared buffers cached
Mem: 773220 766440 6780 0 150436 498588
-/+ buffers/cache: 117416 655804
Swap: 2000084 8040 1992044 |
And the proverbial "wtf" moment (after dd):
Code: | root@laureate:/usr/src/linux# free
total used free shared buffers cached
Mem: 773220 766128 7092 0 150472 499880
-/+ buffers/cache: 115776 657444
Swap: 2000084 8040 1992044
root@laureate:/usr/src/linux# rm /crap
root@laureate:/usr/src/linux# free
total used free shared buffers cached
Mem: 773220 558996 214224 0 150472 290988
-/+ buffers/cache: 117536 655684
Swap: 2000084 8040 1992044
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Notice how all of that "cached" stuff gets freed (and I go from 8mb of memory free to over 100mb).
Anyone else have this problem? I'm still using gentoo-sources-2.4.20-r1 + ptrace fix + ebuild's XFS patch.
I'd really like to fix this!
EDIT: I put my kernel config (/proc/config) at http://www.lovedoesnotexist.com/config.txt |
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Naan Yaar Bodhisattva
Joined: 27 Jun 2002 Posts: 1549
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Posted: Thu Jun 12, 2003 2:02 am Post subject: |
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The last part (re: cached stuff being freed) is not really a problem and is to be expected - when the file is being used, it is going to be cached; once it is removed, the cached stuff can be released.
However, kswapd's behavior seems anomalous. On my gentoo box with the ck6 kernel, everything seems OK: dd chews up CPU during the copy and I don't see kswapd near the top at all. I remember that there were some issues with high CPU usage with kswapd during file i/o... |
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dma Guru
Joined: 31 Jan 2003 Posts: 437 Location: Charlotte, NC, USA
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Posted: Thu Jun 12, 2003 1:20 pm Post subject: |
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Well I've been looking here:
http://www.linux-tutorial.info/cgi-bin/display.pl?311&0&68&0&3
And I've found some interesting stuff.
It seems to do it even after a
It might be that my page and buffer caches are being overused somehow. What is interesting is that kswapd is using all of the CPU and "dd" is using none. Maybe I'll try rebooting when I get back home and see if it does this before I get all of that stuff mapped into memory.
Unless there is another way to unload the page and buffer caches (as seen in "free"). |
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Naan Yaar Bodhisattva
Joined: 27 Jun 2002 Posts: 1549
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Posted: Thu Jun 12, 2003 9:20 pm Post subject: |
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There were several problems reported with kswapd and anomalous high CPU usage. If you do a deja search with "kswapd" and "swapoff" (or other keywords), you will find quite a few.
dma wrote: | ...
It seems to do it even after a
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