Messages in this thread |  | | Date | Fri, 28 Sep 2001 14:58:07 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: 2.4.10 does not set accessed bit for readahead pages |
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On Fri, 28 Sep 2001, Marcelo Tosatti wrote: > > I've done some experiments in the past trying to use a new GFP_ flag for > allocation of readahead pages. This new GFP flag was the indicator to > __alloc_pages() that it should fail very easily (so, in theory, we would > not spend time on page reclaiming for readahead, which is simply a guess).
I don't think the above has anything to do with the accessed bit.
The fact is, failing very easily will mean that we never do much read-ahead at all, or will mean that _other_ allocations will have to bear more of the grunt of the work, and that the LRU lists just become unbalanced. I doubt that the fact that your GFP experiments back up touching the accessed bit.
However, if somebody has benchmarks comparing apples to apples (ie comparing _just_ setting/notsetting the accessed bit), that would be very interesting.
Not setting the accessed bit means that the read-ahead has to be useful within "one loop" of the inactive list. I think that's the right thing: if we don't actually touch the pages soon, the read-ahead was probably a loss. And it's better to cut your losses early rather than late.
Linus
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