From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <3D44F46D.6B619EFB@zip.com.au> Date: Mon, 29 Jul 2002 00:53:17 -0700 From: Andrew Morton MIME-Version: 1.0 Subject: Re: [RFC] start_aggressive_readahead References: <3D44F01A.C7AAA1B4@zip.com.au> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Vladimir Dergachev Cc: linux-mm@kvack.org List-ID: Vladimir Dergachev wrote: > > > > > - It shrinks the window size in response to "misses" - if > > > > userspace requests a page which is *not* inside the previously-requested > > > > window, the future window size is shrunk by 25% > > > > > > This one seems wierd. If I reference a page that could have been in a > > > larger read-ahead window, shouldn't I make the window *larger* so that > > > next time, it *will* be in the window? > > > > That's true. If the application is walking across a file > > touching every fifth page, readahead will stabilise at > > its minimum window size, which is less than five pages and > > we lose bigtime. I'm not sure how to fix that while retaining > > some sanity in the code. > > I am curious: which applications do you know of that actually do this ? None. Just a test program which I used for testing readahead! > What about growing the window even if there is a miss as long as misses > are sequential and not further than a fixed amount from the window ? That would work. If the window size is less than max, and the miss occurred inside the max, increase the window to a size which would have caught that page. Or to the max. - -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/