Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753971Ab3EZOzy (ORCPT ); Sun, 26 May 2013 10:55:54 -0400 Received: from mail-oa0-f53.google.com ([209.85.219.53]:48616 "EHLO mail-oa0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753503Ab3EZOzx (ORCPT ); Sun, 26 May 2013 10:55:53 -0400 MIME-Version: 1.0 In-Reply-To: <20130526135237.GA2333@x61.redhat.com> References: <537407790857e8a5d4db5fb294a909a61be29687.1369529143.git.aquini@redhat.com> <20130526135237.GA2333@x61.redhat.com> From: KOSAKI Motohiro Date: Sun, 26 May 2013 10:55:32 -0400 Message-ID: Subject: Re: [PATCH 01/02] swap: discard while swapping only if SWAP_FLAG_DISCARD_PAGES To: Rafael Aquini Cc: LKML , "linux-mm@kvack.org" , Andrew Morton , Hugh Dickins , shli@kernel.org, Karel Zak , Jeff Moyer , "riel@redhat.com" , Larry Woodman , Mel Gorman 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: 2217 Lines: 44 On Sun, May 26, 2013 at 9:52 AM, Rafael Aquini wrote: > On Sun, May 26, 2013 at 07:44:56AM -0400, KOSAKI Motohiro wrote: >> > + /* >> > + * By flagging sys_swapon, a sysadmin can tell us to >> > + * either do sinle-time area discards only, or to just >> > + * perform discards for released swap page-clusters. >> > + * Now it's time to adjust the p->flags accordingly. >> > + */ >> > + if (swap_flags & SWAP_FLAG_DISCARD_ONCE) >> > + p->flags &= ~SWP_PAGE_DISCARD; >> > + else if (swap_flags & SWAP_FLAG_DISCARD_PAGES) >> > + p->flags &= ~SWP_AREA_DISCARD; >> >> When using old swapon(8), this code turn off both flags, right > > As the flag that enables swap discards SWAP_FLAG_DISCARD remains meaning the > same it meant before, when using old swapon(8) (SWP_PAGE_DISCARD|SWP_AREA_DISCARD) But old swapon(8) don't use neigher SWAP_FLAG_DISCARD_ONCE nor SWAP_FLAG_DISCARD_PAGES. It uses only SWAP_FLAG_DISCARD. So, this condition disables both SWP_PAGE_DISCARD and SWP_AREA_DISCARD. And you changed that SWP_DISCARDABLE is not checked in IO path at all. >- if (si->flags & SWP_DISCARDABLE) { >+ if (si->flags & SWP_PAGE_DISCARD) { I suggest new swapon(8) don't pass SWP_DISCARDABLE and kernel handle SWP_DISCARDABLE as (SWAP_FLAG_DISCARD_ONCE | SWAP_FLAG_DISCARD_PAGES). Optionally, warn SWP_DISCARDABLE is a good idea. > will remain flagged when discard is enabled, so we keep doing discards the same way > we did before (at swapon, and for every released page-cluster). > The flags are removed orthogonally only when the new swapon(8) selects one of the > particular discard policy available by using either SWAP_FLAG_DISCARD_ONCE, > or SWAP_FLAG_DISCARD_PAGES flags. > -- 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/