From: Minchan Kim <firstname.lastname@example.org> To: Andrew Morton <email@example.com> Cc: LKML <firstname.lastname@example.org>, Sergey Senozhatsky <email@example.com>, Joey Pabalinas <firstname.lastname@example.org> Subject: Re: [PATCH v3 7/7] zram: writeback throttle Date: Thu, 29 Nov 2018 10:55:54 +0900 [thread overview] Message-ID: <20181129015554.GC77327@google.com> (raw) In-Reply-To: <email@example.com> On Wed, Nov 28, 2018 at 03:41:41PM -0800, Andrew Morton wrote: > On Tue, 27 Nov 2018 14:54:29 +0900 Minchan Kim <firstname.lastname@example.org> wrote: > > > On small memory system, there are lots of write IO so if we use > > flash device as swap, there would be serious flash wearout. > > To overcome the problem, system developers need to design write > > limitation strategy to guarantee flash health for entire product life. > > > > This patch creates a new konb "writeback_limit" on zram. With that, > > if current writeback IO count(/sys/block/zramX/io_stat) excceds bd_stat > > the limitation, zram stops further writeback until admin can reset > > the limit. > > I'm not really understanding this. Does this only refer to suspending > the idle page writeback feature? Not all zram writeback, surely? It aims for all zram writeback. > > I don't think the documentation gives an administrator sufficient > information to effectively use the feature. Some additional discussion > would help. What sort of values should it be set to and why? > > And what is the default setting? And why? Default setting is 0 so there is no limitation because we couldn't expect user's workload of zram. > > And the limit isn't persistent across reboots which makes me wonder > whether the overall feature is particularly valuable? Good point. Keeping the value in persisten across reboot is userspace's role. I will add this for admin " You could know how many of write happens since the system boot via /sys/block/zramX/bd_stat's bd_writes. If your backing device has wearout concern, you could limit the writing via /sys/block/zramX/writeback_limit. For instance, if the vaule you read bd_writes is 200, you could set 300 to writeback_limit so upcomding 100 write be only allowed. If you set the writeback_limit to lower value than current bd_writes's value, zram allow further writeback without limit. The value will reset when your system reboot so keeping how many write happn until now across reboot is user's job. "
next prev parent reply other threads:[~2018-11-29 1:56 UTC|newest] Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-11-27 5:54 [PATCH v3 0/7] zram idle page writeback Minchan Kim 2018-11-27 5:54 ` [PATCH v3 1/7] zram: fix lockdep warning of free block handling Minchan Kim 2018-11-29 2:43 ` Sergey Senozhatsky 2018-11-27 5:54 ` [PATCH v3 2/7] zram: fix double free backing device Minchan Kim 2018-11-29 2:32 ` Sergey Senozhatsky 2018-11-27 5:54 ` [PATCH v3 3/7] zram: refactoring flags and writeback stuff Minchan Kim 2018-11-27 5:54 ` [PATCH v3 4/7] zram: introduce ZRAM_IDLE flag Minchan Kim 2018-11-29 2:29 ` Sergey Senozhatsky 2018-11-27 5:54 ` [PATCH v3 5/7] zram: support idle/huge page writeback Minchan Kim 2018-11-28 23:35 ` Andrew Morton 2018-11-29 1:36 ` Minchan Kim 2018-11-27 5:54 ` [PATCH v3 6/7] zram: add bd_stat statistics Minchan Kim 2018-11-27 5:54 ` [PATCH v3 7/7] zram: writeback throttle Minchan Kim 2018-11-28 23:41 ` Andrew Morton 2018-11-29 1:55 ` Minchan Kim [this message] 2018-11-29 2:23 ` Sergey Senozhatsky 2018-12-02 23:18 ` Minchan Kim 2018-12-03 2:30 ` Sergey Senozhatsky 2018-12-03 2:41 ` Minchan Kim 2018-12-03 2:45 ` Sergey Senozhatsky 2018-11-30 4:36 ` [PATCH v3 0/7] zram idle page writeback Sergey Senozhatsky 2018-12-02 23:20 ` Minchan Kim 2018-12-02 23:28 ` Joey Pabalinas
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