From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <46AC1297.9030009@redhat.com> Date: Sun, 29 Jul 2007 00:07:51 -0400 From: Rik van Riel MIME-Version: 1.0 Subject: Re: How can we make page replacement smarter (was: swap-prefetch) References: <200707272243.02336.a1426z@gawab.com> <200707280717.41250.a1426z@gawab.com> <46AAEFC4.8000006@redhat.com> <200707281411.57823.a1426z@gawab.com> In-Reply-To: <200707281411.57823.a1426z@gawab.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Al Boldi Cc: Chris Snook , linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: Al Boldi wrote: > Chris Snook wrote: >> At best, reads can be read-ahead and cached, which is why >> sequential swap-in sucks less. On-demand reads are as expensive as I/O >> can get. > > Which means that it should be at least as fast as swap-out, even faster > because write to disk is usually slower than read on modern disks. But > linux currently shows a distinct 2x slowdown for sequential swap-in wrt > swap-out. That's because writes are faster than reads in moderate quantities. The disk caches writes, allowing the OS to write a whole bunch of data into the disk cache and the disk can optimize the IO a bit internally. The same optimization is not possible for reads. -- Politics is the struggle between those who want to make their country the best in the world, and those who believe it already is. Each group calls the other unpatriotic. -- 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/ . Don't email: email@kvack.org