Hi Sergey, > -----Original Message----- > From: owner-linux-mm@xxxxxxxxx [mailto:owner-linux-mm@xxxxxxxxx] On Behalf Of Sergey > Senozhatsky > Sent: Thursday, August 21, 2014 9:05 PM > To: Chao Yu > Cc: 'Minchan Kim'; 'Sergey Senozhatsky'; linux-kernel@xxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx; > ngupta@xxxxxxxxxx; 'Jerome Marchand'; 'Andrew Morton' > Subject: Re: [PATCH] zram: add num_discards for discarded pages stat > > 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 As I know, administrator can send discard request by using "swapon -d /dev/zram0" So after then, notify_free may show the page number mixed with both result of handling REQ_DISCARD and slot free notifications. And as I check the code, there is a workqueue "swap_discard_work" inited in sys_swapon, so maybe there are REQ_DISCARDs sent from background thread, but not filesystem. Is this right? Regards, Yu > > b) the number of pages freed because of REQ_DISCARD notifications > > Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx> > --- > 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<id>/notify_free > Date: August 2010 > Contact: Nitin Gupta <ngupta@xxxxxxxxxx> > 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<id>/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@xxxxxxxxx. 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