Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756842Ab3C2UBm (ORCPT ); Fri, 29 Mar 2013 16:01:42 -0400 Received: from mail-pa0-f45.google.com ([209.85.220.45]:48831 "EHLO mail-pa0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756616Ab3C2UBk (ORCPT ); Fri, 29 Mar 2013 16:01:40 -0400 Date: Fri, 29 Mar 2013 13:01:14 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Minchan Kim cc: Dan Magenheimer , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Seth Jennings , Nitin Gupta , Konrad Rzeszutek Wilk , Shaohua Li , Kamezawa Hiroyuki , Bob Liu Subject: Re: [RFC] mm: remove swapcache page early In-Reply-To: <20130329011801.GA32245@blaptop> Message-ID: References: <1364350932-12853-1-git-send-email-minchan@kernel.org> <433aaa17-7547-4e39-b472-7060ee15e85f@default> <20130328010706.GB22908@blaptop> <5f1504e7-8b07-4109-8271-b214b496ca61@default> <20130329011801.GA32245@blaptop> User-Agent: Alpine 2.00 (LNX 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3913 Lines: 94 On Fri, 29 Mar 2013, Minchan Kim wrote: > On Thu, Mar 28, 2013 at 11:19:12AM -0700, Dan Magenheimer wrote: > > > From: Minchan Kim [mailto:minchan@kernel.org] > > > On Wed, Mar 27, 2013 at 03:24:00PM -0700, Dan Magenheimer wrote: > > > > > From: Hugh Dickins [mailto:hughd@google.com] > > > > > Subject: Re: [RFC] mm: remove swapcache page early > > > > > > > > > > I believe the answer is for frontswap/zmem to invalidate the frontswap > > > > > copy of the page (to free up the compressed memory when possible) and > > > > > SetPageDirty on the PageUptodate PageSwapCache page when swapping in > > > > > (setting page dirty so nothing will later go to read it from the > > > > > unfreed location on backing swap disk, which was never written). > > > > > > > > There are two duplication issues: (1) When can the page be removed > > > > from the swap cache after a call to frontswap_store; and (2) When > > > > can the page be removed from the frontswap storage after it > > > > has been brought back into memory via frontswap_load. > > > > > > > > This patch from Minchan addresses (1). The issue you are raising > > > > > > No. I am addressing (2). > > > > > > > here is (2). You may not know that (2) has recently been solved > > > > in frontswap, at least for zcache. See frontswap_exclusive_gets_enabled. > > > > If this is enabled (and it is for zcache but not yet for zswap), > > > > what you suggest (SetPageDirty) is what happens. > > > > > > I am blind on zcache so I didn't see it. Anyway, I'd like to address it > > > on zram and zswap. > > > > Zswap can enable it trivially by adding a function call in init_zswap. > > (Note that it is not enabled by default for all frontswap backends > > because it is another complicated tradeoff of cpu time vs memory space > > that needs more study on a broad set of workloads.) > > > > I wonder if something like this would have a similar result for zram? > > (Completely untested... snippet stolen from swap_entry_free with > > SetPageDirty added... doesn't compile yet, but should give you the idea.) Thanks for correcting me on zram (in earlier mail of this thread), yes, I was forgetting about the swap_slot_free_notify entry point which lets that memory be freed. > > Nice idea! > > After I see your patch, I realized it was Hugh's suggestion and > you implemented it in proper place. > > Will resend it after testing. Maybe nextweek. > Thanks! Be careful, although Dan is right that something like this can be done for zram, I believe you will find that it needs a little more: either a separate new entry point (not my preference) or a flags arg (or boolean) added to swap_slot_free_notify. Because this is a different operation: end_swap_bio_read() wants to free up zram's compressed copy of the page, but the swp_entry_t must remain valid until swap_entry_free() can clear up the rest. Precisely how much of the work each should do, you will discover. Hugh > > > > > diff --git a/mm/page_io.c b/mm/page_io.c > > index 56276fe..2d10988 100644 > > --- a/mm/page_io.c > > +++ b/mm/page_io.c > > @@ -81,7 +81,17 @@ void end_swap_bio_read(struct bio *bio, int err) > > iminor(bio->bi_bdev->bd_inode), > > (unsigned long long)bio->bi_sector); > > } else { > > + struct swap_info_struct *sis; > > + > > SetPageUptodate(page); > > + sis = page_swap_info(page); > > + if (sis->flags & SWP_BLKDEV) { > > + struct gendisk *disk = sis->bdev->bd_disk; > > + if (disk->fops->swap_slot_free_notify) { > > + SetPageDirty(page); > > + disk->fops->swap_slot_free_notify(sis->bdev, > > + offset); > > + } > > + } > > } > > unlock_page(page); > > bio_put(bio); -- 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/