From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f177.google.com (mail-pd0-f177.google.com [209.85.192.177]) by kanga.kvack.org (Postfix) with ESMTP id 9AFD26B0035 for ; Fri, 22 Aug 2014 02:17:30 -0400 (EDT) Received: by mail-pd0-f177.google.com with SMTP id p10so15488373pdj.36 for ; Thu, 21 Aug 2014 23:17:30 -0700 (PDT) Received: from lgemrelse6q.lge.com (LGEMRELSE6Q.lge.com. [156.147.1.121]) by mx.google.com with ESMTP id cg2si39440220pad.28.2014.08.21.23.17.28 for ; Thu, 21 Aug 2014 23:17:29 -0700 (PDT) Date: Fri, 22 Aug 2014 15:18:05 +0900 From: Minchan Kim Subject: Re: [PATCH] zram: add num_discards for discarded pages stat Message-ID: <20140822061805.GI17372@bbox> References: <001201cfb838$fb0ac4a0$f1204de0$@samsung.com> <20140815061138.GA940@swordfish> <002d01cfbb70$ea7410c0$bf5c3240$@samsung.com> <20140819112500.GA2484@swordfish> <20140820020924.GD32620@bbox> <006701cfbc4f$c9d2fe00$5d78fa00$@samsung.com> <20140821011854.GE17372@bbox> <001601cfbd1f$b9f068d0$2dd13a70$@samsung.com> <20140821130504.GB946@swordfish> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20140821130504.GB946@swordfish> Sender: owner-linux-mm@kvack.org List-ID: To: Sergey Senozhatsky Cc: Chao Yu , linux-kernel@vger.kernel.org, linux-mm@kvack.org, ngupta@vflare.org, 'Jerome Marchand' , 'Andrew Morton' Hi Sergey, On Thu, Aug 21, 2014 at 10:05:04PM +0900, Sergey Senozhatsky wrote: > On (08/21/14 17:09), Chao Yu wrote: > [cut] > > > > > > I hope I'm not discouraging. :) > > > > Nope, please let me try again, :) > > > > Since we have supported handling discard request in this commit > > f4659d8e620d08bd1a84a8aec5d2f5294a242764 (zram: support REQ_DISCARD), zram got > > one more chance to free unused memory whenever received discard request. But > > without stating for discard request, there is no method for user to know whether > > discard request has been handled by zram or how many blocks were discarded by > > zram when user wants to know the effect of discard. > > > > In this patch, we add num_discards to stat discarded pages, and export it to > > sysfs for users. > > > > In other words, here is my proposal: > > -----8<-----8<----- > > Subject: [PATCH] zram: use notify_free to account all free notifications > > notify_free device attribute accounts the number of slot free notifications > and internally represents the number of zram_free_page() calls. Slot free > notifications are sent only when device is used as a swap device, hence > notify_free is used only for swap devices. Since f4659d8e620d08 (zram: > support REQ_DISCARD) ZRAM handles yet another one free notification (also > via zram_free_page() call) -- REQ_DISCARD requests, which are sent by a > filesystem, whenever some data blocks are discarded. However, there is no > way to know the number of notifications in the latter case. > > Use notify_free to account the number of pages freed in zram_free_page(), > instead of accounting only swap_slot_free_notify() calls (each > zram_slot_free_notify() call frees one page). > > This means that depending on usage scenario notify_free represents: > a) the number of pages freed because of slot free notifications, which is > equal to the number of swap_slot_free_notify() calls, so there is no > behaviour change > > b) the number of pages freed because of REQ_DISCARD notifications IMO, it would be better to separate it because zram-swap does both free notify and discard but trigger timing is different so we could measure which one is better if we want to replace swap_slot_free_notify with discard. So I'd like to keep both and then we could remove notify_free later once we prove discard alone is enough. What do you think about it? > > Signed-off-by: Sergey Senozhatsky > --- > Documentation/ABI/testing/sysfs-block-zram | 13 ++++++++----- > drivers/block/zram/zram_drv.c | 2 +- > 2 files changed, 9 insertions(+), 6 deletions(-) > > diff --git a/Documentation/ABI/testing/sysfs-block-zram b/Documentation/ABI/testing/sysfs-block-zram > index 70ec992..73ed400 100644 > --- a/Documentation/ABI/testing/sysfs-block-zram > +++ b/Documentation/ABI/testing/sysfs-block-zram > @@ -77,11 +77,14 @@ What: /sys/block/zram/notify_free > Date: August 2010 > Contact: Nitin Gupta > Description: > - The notify_free file is read-only and specifies the number of > - swap slot free notifications received by this device. These > - notifications are sent to a swap block device when a swap slot > - is freed. This statistic is applicable only when this disk is > - being used as a swap disk. > + The notify_free file is read-only. Depending on device usage > + scenario it may account a) the number of swap slot free > + notifications or b) the number of REQ_DISCARD requests sent > + by bio. The former ones are sent to a swap block device when a > + swap slot is freed, which implies that this disk is being used > + as a swap disk. The latter ones are sent by filesystem mounted > + with discard option, whenever some data blocks are getting > + discarded. > > What: /sys/block/zram/zero_pages > Date: August 2010 > diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c > index d00831c..c2e7127 100644 > --- a/drivers/block/zram/zram_drv.c > +++ b/drivers/block/zram/zram_drv.c > @@ -344,6 +344,7 @@ static void zram_free_page(struct zram *zram, size_t index) > atomic64_sub(zram_get_obj_size(meta, index), > &zram->stats.compr_data_size); > atomic64_dec(&zram->stats.pages_stored); > + atomic64_inc(&zram->stats.notify_free); > > meta->table[index].handle = 0; > zram_set_obj_size(meta, index, 0); > @@ -843,7 +844,6 @@ static void zram_slot_free_notify(struct block_device *bdev, > bit_spin_lock(ZRAM_ACCESS, &meta->table[index].value); > zram_free_page(zram, index); > bit_spin_unlock(ZRAM_ACCESS, &meta->table[index].value); > - atomic64_inc(&zram->stats.notify_free); > } > > static const struct block_device_operations zram_devops = { > -- > 2.1.0.233.g9eef2c8 > > -- > 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 -- Kind regards, Minchan Kim -- 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