Messages in this thread | | | Date | Sat, 19 May 2007 20:30:31 +0800 | From | Fengguang Wu <> | Subject | Re: [PATCH 1/9] readahead: introduce PG_readahead |
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On Fri, May 18, 2007 at 11:28:24PM -0700, Andrew Morton wrote: > On Thu, 17 May 2007 06:47:53 +0800 Fengguang Wu <wfg@mail.ustc.edu.cn> wrote: > > > Introduce a new page flag: PG_readahead. > > Is there any way in which we can avoid adding a new page flag? > > We have the advantage that if the kernel very occasionally gets the wrong > result for PageReadahead(page), nothing particularly bad will happen, so we > can do racy things. > > >From a quick peek, it appears that PG_readahead is only ever set against > non-uptodate pages. If true we could perhaps exploit that: say, > PageReadahead(page) == PG_referenced && !PG_uptodate?
PG_uptodate will flip to 1 before the reader touches the page :(
However, it may be possible to share the same bit with PG_reclaim or PG_booked. Which one would be preferred?
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