On Wed, May 27, 2009 at 04:45:53AM -0700, David G Lawrence wrote: > I'm wondering if you have a low limit on how far you will reduce > the dirhash. In a system that is thrashing a bit (due to a large process, > for example), I can imagine multiple (10+) calls to the lowmem handler in > rapid succession that would completely deplete the dirhash. Seems like > this would result in even worse thrashing as more disk I/O occurs due > to lack of dirhash. The idea of resisting recycling recently used hashes is supposed to give us some protection against thrashing. We talked about the problem with Alan for a bit, and reached the conclusion that it was probably best to return some memory each time the lowmem handler was called. If this turns out to be a problem, I guess we could add a low water mark, where if dirhash holds less than that memory then it won't return the memory on a low memory event. (Note that under normal circumstances, there is some protection against thrashing because of the recycling schemem used.) David.Received on Wed May 27 2009 - 17:05:16 UTC
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