Messages in this thread | | | Date | Tue, 17 Nov 1998 07:42:12 +0100 (CET) | From | Rik van Riel <> | Subject | Re: unexpected paging during large file reads in 2.1.127 |
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On Mon, 16 Nov 1998, Stephen C. Tweedie wrote: > On Mon, 16 Nov 1998 21:48:35 +0100 (CET), Rik van Riel > <H.H.vanRiel@phys.uu.nl> said: > > On Mon, 16 Nov 1998, Stephen C. Tweedie wrote: > >> The real cure is to disable page aging in the page cache completely. > >> Now that we have disabled it for swap, it makes absolutely no sense at > >> all to keep it in the page cache. > > > This is not entirely true. There is a major difference > > between pages in the page cache and pages that can go > > into swap. The latter kind will always be mapped inside > > the address space of a program (where it gets proper > > aging and stuff) > > No it doesn't, that's what I'm saying. Linus removed swap page aging in > the recent kernels. That throws the balance between swap and cache > completely out of the window: removing the page cache aging is necessary > to restore balance. There are many many reports of massive cache growth > on the latest kernels as a result of this.
I meant the page aging that occurs in vmscan.c, where we decide on which page to unmap from a program's address space. There we do aging while we don't age pages from files that are read().
> > Now we can get severe problems with readahead when we > > are evicting just read-in data because it isn't mapped, > > No, we don't. We don't evict just-read-in data, because we mark such > pages as PG_Referenced. It takes two complete shrink_mmap() passes > before we can evict such pages.
OK, I can (and have for quite a while) agree with this. Kernels with this feature and enough memory will run great, maybe small machines (<16M) will have a bit of trouble keeping up readahead performance (since kswapd will have made it's round a bit fast) but those machines will have sucky performance anyway :)
Rik -- slowly getting used to dvorak kbd layout... +-------------------------------------------------------------------+ | Linux memory management tour guide. H.H.vanRiel@phys.uu.nl | | Scouting Vries cubscout leader. http://www.phys.uu.nl/~riel/ | +-------------------------------------------------------------------+
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