Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751713Ab0KWJFY (ORCPT ); Tue, 23 Nov 2010 04:05:24 -0500 Received: from mail-iw0-f174.google.com ([209.85.214.174]:48671 "EHLO mail-iw0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750794Ab0KWJFV (ORCPT ); Tue, 23 Nov 2010 04:05:21 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; b=VA3rjMTNFUHYMwdT9TGl+d6aHR045RYMgGt8XOa1RwsiGayi91VtEh8KsIBE0HgVZt EqFRTHPe7sy9hzEAKYah3RfEvgSTn1BAHugq83nAW8sXyaZVLjjRi7HMsHvJn90RPXBD GqdE/JD+Up4jC1Y+FWPJaiVcOeMIxf/f0j3Aw= MIME-Version: 1.0 In-Reply-To: <20101123175948.7BD1.A69D9226@jp.fujitsu.com> References: <20101123165240.7BC2.A69D9226@jp.fujitsu.com> <20101123175948.7BD1.A69D9226@jp.fujitsu.com> Date: Tue, 23 Nov 2010 18:05:20 +0900 Message-ID: Subject: Re: [RFC 1/2] deactive invalidated pages From: Minchan Kim To: KOSAKI Motohiro Cc: Andrew Morton , linux-mm , LKML , Peter Zijlstra , Rik van Riel , Johannes Weiner , Nick Piggin Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2204 Lines: 53 On Tue, Nov 23, 2010 at 6:02 PM, KOSAKI Motohiro wrote: >> On Tue, Nov 23, 2010 at 5:01 PM, KOSAKI Motohiro >> wrote: >> >> Hi KOSAKI, >> >> >> >> 2010/11/23 KOSAKI Motohiro : >> >> >> By Other approach, app developer uses POSIX_FADV_DONTNEED. >> >> >> But it has a problem. If kernel meets page is writing >> >> >> during invalidate_mapping_pages, it can't work. >> >> >> It is very hard for application programmer to use it. >> >> >> Because they always have to sync data before calling >> >> >> fadivse(..POSIX_FADV_DONTNEED) to make sure the pages could >> >> >> be discardable. At last, they can't use deferred write of kernel >> >> >> so that they could see performance loss. >> >> >> (http://insights.oetiker.ch/linux/fadvise.html) >> >> > >> >> > If rsync use the above url patch, we don't need your patch. >> >> > fdatasync() + POSIX_FADV_DONTNEED should work fine. >> >> >> >> It works well. But it needs always fdatasync before calling fadvise. >> >> For small file, it hurt performance since we can't use the deferred write. >> > >> > I doubt rsync need to call fdatasync. Why? >> > >> > If rsync continue to do following loop, some POSIX_FADV_DONTNEED >> > may not drop some dirty pages. But they can be dropped at next loop's >> > POSIX_FADV_DONTNEED. Then, It doesn't make serious issue. >> > >> > 1) read >> > 2) write >> > 3) POSIX_FADV_DONTNEED >> > 4) goto 1 >> >> fadvise need pair (offset and len). >> if the pair in next turn is different with one's previous turn, it >> couldn't be dropped. > > invalidate_mapping_pages() are using pagevec_lookup() and pagevec_lookup() > are using radix tree lookup. Then, Even if rsync always use [0, inf) pair, I don't think > it makes much slowdown. > I mean fdatasync causes slowdown, not fadvise. if you fadvise(don't need) without fdatasync, you could loss the data. -- Kind regards, Minchan Kim -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/