Messages in this thread | | | Date | Thu, 7 Jan 1999 11:33:49 -0800 (PST) | From | Linus Torvalds <> | Subject | Re: Results: 2.2.0-pre5 vs arcavm10 vs arcavm9 vs arcavm7 |
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On 7 Jan 1999, Zlatko Calusic wrote: > > 1) Swap performance in pre-5 is much worse compared to pre-4 in > *certain* circumstances. I'm using quite stupid and unintelligent > program to check for raw swap speed (attached below). With 64 MB of > RAM I usually run it as 'hogmem 100 3' and watch for result which is > recently around 6 MB/sec. But when I lately decided to start two > instances of it like "hogmem 50 3 & hogmem 50 3 &" in pre-4 I got 2 x > 2.5 MB/sec and in pre-5 it is only 2 x 1 MB/sec and disk is making > very weird and frightening sounds. My conclusion is that now (pre-5) > system behaves much poorer when we have more than one thrashing > task. *Please*, check this, it is a quite serious problem.
Ok, will investigate. One thing you can test is to try out different "count" arguments to try_to_free_pages() (this was part of what Andrea did, btw). So instead of (page_alloc.c, line 285):
freed = try_to_free_pages(gfp_mask, SWAP_CLUSTER_MAX);
you can try different things for the second argument: the thing Andrea did was something like
freed = try_to_free_pages(gfp_mask, freepages.high - nr_free_pages);
which could work well (one thing I'm nervous about is that this probably needs to be limited some way - it can be quite a large number on large machines, and that's why I'd like to hear comments from people).
> 2) In pre-5, under heavy load, free memory is hovering around > freepages.min instead of being somewhere between freepages.low & > freepages.max. This could make trouble for bursts of atomic > allocations (networking!).
The change above would change this too.
> 3) Nitpick #1: /proc/swapstats exist but is only filled with > zeros. Probably it should go away. I believe Stephen added it > recently, but only part of his patch got actually applied.
Maybe somebody can find a use for it.
> 4) Nitpick #2": "Swap cache:" line in report of Alt-SysRq-M is not > useful as it is laid now. People have repeatedly sent patches (Rik, > Andrea...) to fix this but it is still not fixed, as of pre-5.
I never use it, so it hasn't been a big issue.
> 5) There is lots of #if 0 constructs in MM code, and also lots of > structures are not anymore used but still take precious memory in > compiled kernel and uncover itself under /proc (/proc/sys/vm/swapctl > for instance). Do you want a patch to remove this cruft?
Some of the #if 0 code should certainly be removed. Some of it is useful as a kind of commentary - sometimes code is removed not because it doesn't make sense, but because the implementation wasn't quite good enough.
Linus
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