Messages in this thread | | | From | Daniel Phillips <> | Subject | Re: [resent PATCH] Re: very slow parallel read performance | Date | Sun, 26 Aug 2001 18:55:04 +0200 |
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On August 25, 2001 06:28 pm, pcg@goof.com ( Marc) (A.) (Lehmann ) wrote: > On Sat, Aug 25, 2001 at 12:50:51PM -0300, Rik van Riel <riel@conectiva.com.br> wrote: > > Remember NL.linux.org a few weeks back, where a difference of > > 10 FTP users more or less was the difference between a system > > load of 3 and a system load of 250 ? ;) > > OTOH, servers the use a single process or thread per connection are > destined to fail under load ;)
There's an obvious explanation for the high loadavg people are seeing when their systems go into thrash mode: when free is exhausted, every task that fails to get a block in __alloc_pages will become PF_MEMALLOC and start scanning. The remaining tasks that are still running will soon also fail in __alloc_pages and jump onto the dogpile. This is a pretty clear demonstration of why the current "self-help" strategy is flawed.
Those tasks that can't get memory should block, leaving one or two threads to sort things out under predictable conditions, then restart the blocked threads as appropriate.
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