Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753354AbcC1E5M (ORCPT ); Mon, 28 Mar 2016 00:57:12 -0400 Received: from LGEAMRELO11.lge.com ([156.147.23.51]:43486 "EHLO lgeamrelo11.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751643AbcC1E5D (ORCPT ); Mon, 28 Mar 2016 00:57:03 -0400 X-Original-SENDERIP: 156.147.1.125 X-Original-MAILFROM: minchan@kernel.org X-Original-SENDERIP: 165.244.98.203 X-Original-MAILFROM: minchan@kernel.org X-Original-SENDERIP: 10.177.223.161 X-Original-MAILFROM: minchan@kernel.org Date: Mon, 28 Mar 2016 13:58:38 +0900 From: Minchan Kim To: Andrew Morton CC: LKML , Sergey Senozhatsky , karam.lee@lge.com, sangseok.lee@lge.com, chan.jeong@lge.com, Joonsoo Kim Subject: Re: [PATCH] zram: revive swap_slot_free_notify Message-ID: <20160328045838.GB31023@bbox> MIME-Version: 1.0 User-Agent: Mutt/1.5.21 (2010-09-15) X-MIMETrack: Itemize by SMTP Server on LGEKRMHUB08/LGE/LG Group(Release 8.5.3FP6|November 21, 2013) at 2016/03/28 13:56:59, Serialize by Router on LGEKRMHUB08/LGE/LG Group(Release 8.5.3FP6|November 21, 2013) at 2016/03/28 13:56:59, Serialize complete at 2016/03/28 13:56:59 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 9431 Lines: 216 On Wed, Mar 23, 2016 at 01:45:34PM +0900, Joonsoo Kim wrote: > On Tue, Mar 22, 2016 at 11:06:29PM +0900, Minchan Kim wrote: > > On Tue, Mar 22, 2016 at 05:20:08PM +0900, Joonsoo Kim wrote: > > > 2016-03-22 17:00 GMT+09:00 Minchan Kim : > > > > On Tue, Mar 22, 2016 at 02:08:59PM +0900, Joonsoo Kim wrote: > > > >> On Fri, Mar 18, 2016 at 04:58:31PM +0900, Minchan Kim wrote: > > > >> > "remove compressed copy from zram in-memory" > > > >> > applied swap_slot_free_notify call in *end_swap_bio_read* to > > > >> > remove duplicated memory between zram and memory. > > > >> > > > > >> > However, with introducing rw_page in zram <8c7f01025f7b> > > > >> > "zram: implement rw_page operation of zram", it became void > > > >> > because rw_page doesn't need bio. > > > >> > > > > >> > This patch restores the function for rw_page. > > > >> > > > > >> > Signed-off-by: Minchan Kim > > > >> > --- > > > >> > mm/page_io.c | 93 ++++++++++++++++++++++++++++++++---------------------------- > > > >> > 1 file changed, 50 insertions(+), 43 deletions(-) > > > >> > > > > >> > diff --git a/mm/page_io.c b/mm/page_io.c > > > >> > index ff74e512f029..18aac7819cc9 100644 > > > >> > --- a/mm/page_io.c > > > >> > +++ b/mm/page_io.c > > > >> > @@ -66,6 +66,54 @@ void end_swap_bio_write(struct bio *bio) > > > >> > bio_put(bio); > > > >> > } > > > >> > > > > >> > +static void swap_slot_free_notify(struct page *page) > > > >> > +{ > > > >> > + struct swap_info_struct *sis; > > > >> > + struct gendisk *disk; > > > >> > + > > > >> > + /* > > > >> > + * There is no guarantee that the page is in swap cache - the software > > > >> > + * suspend code (at least) uses end_swap_bio_read() against a non- > > > >> > + * swapcache page. So we must check PG_swapcache before proceeding with > > > >> > + * this optimization. > > > >> > + */ > > > >> > + if (unlikely(!PageSwapCache(page))) > > > >> > + return; > > > >> > + > > > >> > + sis = page_swap_info(page); > > > >> > + if (!(sis->flags & SWP_BLKDEV)) > > > >> > + return; > > > >> > + > > > >> > + /* > > > >> > + * The swap subsystem performs lazy swap slot freeing, > > > >> > + * expecting that the page will be swapped out again. > > > >> > + * So we can avoid an unnecessary write if the page > > > >> > + * isn't redirtied. > > > >> > + * This is good for real swap storage because we can > > > >> > + * reduce unnecessary I/O and enhance wear-leveling > > > >> > + * if an SSD is used as the as swap device. > > > >> > + * But if in-memory swap device (eg zram) is used, > > > >> > + * this causes a duplicated copy between uncompressed > > > >> > + * data in VM-owned memory and compressed data in > > > >> > + * zram-owned memory. So let's free zram-owned memory > > > >> > + * and make the VM-owned decompressed page *dirty*, > > > >> > + * so the page should be swapped out somewhere again if > > > >> > + * we again wish to reclaim it. > > > >> > + */ > > > >> > + disk = sis->bdev->bd_disk; > > > >> > + if (disk->fops->swap_slot_free_notify) { > > > >> > + swp_entry_t entry; > > > >> > + unsigned long offset; > > > >> > + > > > >> > + entry.val = page_private(page); > > > >> > + offset = swp_offset(entry); > > > >> > + > > > >> > + SetPageDirty(page); > > > >> > + disk->fops->swap_slot_free_notify(sis->bdev, > > > >> > + offset); > > > >> > + } > > > >> > +} > > > >> > + > > > >> > static void end_swap_bio_read(struct bio *bio) > > > >> > { > > > >> > struct page *page = bio->bi_io_vec[0].bv_page; > > > >> > @@ -81,49 +129,7 @@ static void end_swap_bio_read(struct bio *bio) > > > >> > } > > > >> > > > > >> > SetPageUptodate(page); > > > >> > - > > > >> > - /* > > > >> > - * There is no guarantee that the page is in swap cache - the software > > > >> > - * suspend code (at least) uses end_swap_bio_read() against a non- > > > >> > - * swapcache page. So we must check PG_swapcache before proceeding with > > > >> > - * this optimization. > > > >> > - */ > > > >> > - if (likely(PageSwapCache(page))) { > > > >> > - struct swap_info_struct *sis; > > > >> > - > > > >> > - sis = page_swap_info(page); > > > >> > - if (sis->flags & SWP_BLKDEV) { > > > >> > - /* > > > >> > - * The swap subsystem performs lazy swap slot freeing, > > > >> > - * expecting that the page will be swapped out again. > > > >> > - * So we can avoid an unnecessary write if the page > > > >> > - * isn't redirtied. > > > >> > - * This is good for real swap storage because we can > > > >> > - * reduce unnecessary I/O and enhance wear-leveling > > > >> > - * if an SSD is used as the as swap device. > > > >> > - * But if in-memory swap device (eg zram) is used, > > > >> > - * this causes a duplicated copy between uncompressed > > > >> > - * data in VM-owned memory and compressed data in > > > >> > - * zram-owned memory. So let's free zram-owned memory > > > >> > - * and make the VM-owned decompressed page *dirty*, > > > >> > - * so the page should be swapped out somewhere again if > > > >> > - * we again wish to reclaim it. > > > >> > - */ > > > >> > - struct gendisk *disk = sis->bdev->bd_disk; > > > >> > - if (disk->fops->swap_slot_free_notify) { > > > >> > - swp_entry_t entry; > > > >> > - unsigned long offset; > > > >> > - > > > >> > - entry.val = page_private(page); > > > >> > - offset = swp_offset(entry); > > > >> > - > > > >> > - SetPageDirty(page); > > > >> > - disk->fops->swap_slot_free_notify(sis->bdev, > > > >> > - offset); > > > >> > - } > > > >> > - } > > > >> > - } > > > >> > - > > > >> > + swap_slot_free_notify(page); > > > >> > out: > > > >> > unlock_page(page); > > > >> > bio_put(bio); > > > >> > @@ -347,6 +353,7 @@ int swap_readpage(struct page *page) > > > >> > > > > >> > ret = bdev_read_page(sis->bdev, swap_page_sector(page), page); > > > >> > if (!ret) { > > > >> > + swap_slot_free_notify(page); > > > >> > count_vm_event(PSWPIN); > > > >> > return 0; > > > >> > } > > > >> > > > >> Hello, > > > > > > > > Hey Joonsoo, > > > > > > > >> > > > >> You need to check PageUpdate() or something because bdev_read_page() > > > >> can be asynchronous. > > > > > > > > I considered it but decided not to add the check :(. > > > > Because I couldn't justify what benfit we can have with the check. > > > > The swap_slot_free_notify is tightly coupled with zram for several > > > > years and zram have been worked synchronously. So if bdev_read_page > > > > returns 0, it means we already have read the page successfully. > > > > Even, when I looked up other rw_page user, it seems there is no async > > > > rw_page users at the moment. > > > > > > Yes, I also looked up other rw_page users and found that > > > there is no async rw_page now. > > > > > > > If there is someone want to use *async* rw_page && *swap_slot_free_noity* > > > > in future, we could add the check easily. But I hope anyone never use > > > > swap_slot_free_notify any more which is mess. :( > > > > > > But, I think that we should add the check. If someone want it, how does > > > he/she know about it? Even, if someone makes zram to read/write > > > asynchronously, we can miss it easily. This is error-prone practice. > > > > Okay, I don't have strong against it. > > If we really want to catch such case, let's add WARN_ON_ONCE. > > I'm okay with it. But, please add code comment why WARN_ON_ONCE() is > added here. > > Then, > Acked-by: Joonsoo Kim > > Thanks. >From 45a05828a83eb6111230801a60ff973aa7ed3ebf Mon Sep 17 00:00:00 2001 From: Minchan Kim Date: Mon, 28 Mar 2016 13:34:50 +0900 Subject: [PATCH] mm: catch swap_slot_free_notify's misuse swap_slot_free_notify works with synchronous rw_page driver(i.e, zram) but someday, if someone implements asynchonous rw_page driver and he want to hook swap_slot_free_notify to remove dulicate memory, it will break current swap_slot_free_notify. This patch catches the situation. Signed-off-by: Minchan Kim Acked-by: Joonsoo Kim --- mm/page_io.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/mm/page_io.c b/mm/page_io.c index 18aac7819cc9..32c82cdbed8e 100644 --- a/mm/page_io.c +++ b/mm/page_io.c @@ -105,6 +105,13 @@ static void swap_slot_free_notify(struct page *page) swp_entry_t entry; unsigned long offset; + /* + * If a driver supports async rw_page and + * swap_slot_free_notify, swap_slot_free_notify + * will not work rightly. + */ + WARN_ON_ONCE(!PageUptodate(page)); + entry.val = page_private(page); offset = swp_offset(entry); -- 1.9.1