[From nobody Thu Jun 25 05:55:59 2020 Received: from delta.hotplug.ru ([2a04:ac00:1:3dd8::10]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1joNow-0003qW-BU for openwrt-devel@lists.openwrt.org; Thu, 25 Jun 2020 09:05:23 +0000 Received: from [192.168.168.60] (0890868029.static.corbina.ru [89.179.126.107]) by delta.hotplug.ru (Postfix) with ESMTPSA id AC5AE105617; Thu, 25 Jun 2020 12:05:07 +0300 (MSK) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=hotplug.ru; s=mx; t=1593075907; bh=ou4YNMTkMTFUEm0dSUCCwJfk8SfbXoabvYzJpCj/FJ4=; h=Subject:To:Cc:References:From:Date:In-Reply-To; b=EU4qvcewpfhjn52QHLUcttIsY2XxxnBNq3O+NGpn6L+6aOXcIHLi+7NMiCDRF2d3T DugkytGrZyK49oRNB4uPXuVpr/afYw2ZwiqTwYv5L3YHdZ0XKOXuu1zJr3s39WhSjI b3Xp1e1soAqj+29+OD4JTlrPvHIE1CUrmiXFPcrc= Subject: Re: [PATCH] zram-swap: enable swap discard To: Rui Salvaterra <rsalvaterra@gmail.com> Cc: openwrt-devel@lists.openwrt.org, john@phrozen.org References: <20200623112953.3454-1-rsalvaterra@gmail.com> <c4539e18-8d09-3e22-055c-502465252e43@hotplug.ru> <CALjTZvbX-Nt5umO1iprg-JVo2TR+u8TM2f7DY7gQJ25VNQW7fg@mail.gmail.com> From: Emil Muratov <gpm@hotplug.ru> Message-ID: <9948ad5b-26d1-446e-cbe6-d66bca677721@hotplug.ru> Date: Thu, 25 Jun 2020 12:05:07 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <CALjTZvbX-Nt5umO1iprg-JVo2TR+u8TM2f7DY7gQJ25VNQW7fg@mail.gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-GB X-Spam-Note: CRM114 invocation failed X-Spam-Score: -0.2 (/) X-Spam-Report: SpamAssassin version 3.4.4 on merlin.infradead.org summary: Content analysis details: (-0.2 points) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 SPF_PASS SPF: sender matches SPF record -0.0 SPF_HELO_PASS SPF: HELO matches SPF record -0.1 DKIM_VALID Message has at least one valid DKIM or DK signature 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily valid -0.1 DKIM_VALID_EF Message has a valid DKIM or DK signature from envelope-from domain -0.1 DKIM_VALID_AU Message has a valid DKIM or DK signature from author's domain Hmm... that looks weird at first, I was checking kernel counters at /sys/block/zram0/io_stat, which is zram device for swap. And if there was positive counter for discards for zram device while swap was not sending any discards than what is that counter is about? Have you checked if stressing swap with some push/pull paging load indeed keeps ram occupied at max level? Analyzing /sys/block/$zdev/mm_stat could also help there. I do not remember mem leaks issues when tested stats script, but who knows... Need to take a closer look into this. Thanks! On 25.06.2020 01:39, Rui Salvaterra wrote: > Hi, Emil, > > On Wed, 24 Jun 2020 at 20:30, Emil Muratov <gpm@hotplug.ru> wrote: >> zram swap discard is enabled by default, no need to specify additional >> option. Pls, check for example info output in >> https://github.com/openwrt/openwrt/pull/1515 > Unfortunately, that's not quite right. This has nothing to do with > zram itself, but with the way swapon syscall works. Yes, both discard > *policies* are enabled by default if, *and only if* the syscall is > invoked with *only* the SWAP_FLAG_DISCARD flag set [1]. > Anyway, it's easy to see if the swap device is issuing trim/discard > commands. For example, on my router, with my patch: > > root@heimdal:~# dmesg | grep swap > [ 12.302928] Adding 1036284k swap on /dev/zram0. Priority:-2 > extents:1 across:1036284k SSDsc > root@heimdal:~# > > According to the relevant section of the kernel source code [2], The > last letters, SSDsc mean: > SS: solid state (obviously, it's a RAM-based device) > D: supports discard > s: area-based discard is enabled > c: page-based discard is enabled > > Consequently, if a system only shows SS, discard commands aren't being issued. > > [1] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/include/linux/swap.h?h=linux-4.14.y#n24 > [2] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/mm/swapfile.c?h=linux-4.14.y#n3283 > > Cheers, > Rui ]