RE: [PATCH] zram: add num_discards for discarded pages stat
From: Chao Yu <hidden>
Date: 2014-08-26 02:44:25
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Hi Sergey,
-----Original Message----- From: owner-linux-mm@kvack.org [mailto:owner-linux-mm@kvack.org] On Behalf Of Sergey Senozhatsky Sent: Thursday, August 21, 2014 9:05 PM To: Chao Yu Cc: 'Minchan Kim'; 'Sergey Senozhatsky'; linux-kernel@vger.kernel.org; linux-mm@kvack.org; ngupta@vflare.org; '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]quoted
quoted
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
quoted hunk ↗ jump to hunk
b) the number of pages freed because of REQ_DISCARD notifications Signed-off-by: Sergey Senozhatsky <redacted> --- 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-zramb/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@vflare.org> 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 2010diff --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: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
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