On Sat, 19 May 2007 20:30:31 +0800 Fengguang Wu <wfg@xxxxxxxxxxxxxxxx> wrote: > 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@xxxxxxxxxxxxxxxx> 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 :( OK. > However, it may be possible to share the same bit with PG_reclaim or PG_booked. > Which one would be preferred? I'd like PG_booked to go away too - I don't think we've put that under the microscope yet. If it remains then its scope will be "defined by the filesystem", so readahead shouldn't use it. PG_reclaim belongs to core VFS so that's much better. Let's not do anything ugly, slow or silly in there, but please do take a look, see if there is an opportunity here. - To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
