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Wed, 22 May 2019 08:19:38 -0700 (PDT) Received: from mavoffice.ixsystems.com ([12.189.233.129]) by smtp.gmail.com with ESMTPSA id v144sm6406295ywv.15.2019.05.22.08.19.38 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 22 May 2019 08:19:38 -0700 (PDT) Sender: Alexander Motin Subject: Re: Commit r345200 (new ARC reclamation threads) looks suspicious to me - second potential problem To: Mark Johnston , Lev Serebryakov Cc: freebsd-fs@freebsd.org, freebsd-hackers@freebsd.org References: <369cb1e9-f36a-a558-6941-23b9b811825a@FreeBSD.org> <20190520164202.GA2130@spy> From: Alexander Motin Openpgp: preference=signencrypt Autocrypt: addr=mav@FreeBSD.org; prefer-encrypt=mutual; keydata= xsBNBFOzxAwBCADkPrax0pI2W/ig0CK9nRJJwsHitAGEZ2HZiFEuti+6/4UVxj81yr4ak/4g 9bKUyC7rMEAp/ZHNhd+MFCPAAcHPvtovnfykqE/vuosCS3wlSLloix2iKVLks0CwbLHGAyne 46lTQW74Xl/33c3W1Z6d8jD9gVFT/xaVzZ0U9xdzOmsYAZaAj4ki0tuxO9F7L+ct9grRe7iP g8t9hai7BL4ee3VRwk2JXnKb7UvBiVITKYWKz1jRvZIrjPokgEcCLOSlv7x/1kjuFnj3xWZU 7HSFFT8J93epBbrSSCsYsppIk2fZH41kaaFXsMQfTPH8wkeM6qwrvOh4HiQM08R+9tThABEB AAHNIUFsZXhhbmRlciBNb3RpbiA8bWF2QEZyZWVCU0Qub3JnPsLAlwQTAQoAQQIbAwULCQgH AwUVCgkICwUWAwIBAAIeAQIXgAIZARYhBOmM88TmnMPNDledVYMYw5VbqyJ/BQJZYMKuBQkN McyiAAoJEIMYw5VbqyJ/tuUIAOG3ONOSNYqjK4eTZ1TVh9jdUBAhWk5nhDFnODN49Wj0AbYm 7aIqy8O1hnCDSZG5LttjSAo3UfXJZDKQM0BLb0gpRMBnAYqO6tdolLNqAbPGJBnGoPjsh24y 6KcbDaNnis+lD4GwPXwQM+92wZGhCUFElPV9NciZGVS65TNIgk7X+yEjjhD1MSWKKijZ1r9Z zIt4OzUTxxNOvzdlABZS88nNRdJkatOQJPmFdd1mpP6UzTNCiLUo1pIqOEtJgvVVDYq5WHY6 tciWWYdmZG/tIBexJmv2mV2OLVjXR6ZeKmntVH14H72/wRHJuYHQC+r5SVRcWWayrThsY6jZ Yr4+raTOwE0EU7PEDAEIAOZgWf2cJIu+58IzP2dkXE/urj3tr4OqrB/yHGWUf71Lz6D0Fi6Z AXgDtmcFLGPfMyWuLAvSM+xmoguk7zC4hRBYvQycmIhuqBq1jO1Wp/Z+lpoPM/1cDYLn8Flv mI/c40MhUZh345DA4jYWWaZNjQHUWVQ1fPf595vdVVMPT/abE8E5DaF6fSkRmqFTmfYRkfbt 3ytU8NdUapDcJVY7cEP2nJBVNZPnOIObR/ZIgSxjjrG5o34yXoqeup8JvwEv+/NylzzuyXEZ R1EdEIzQ/a1nh/0j4NXtzZEqKW4aTWlmSqb6wN8jh1OSOOqkYsfnE3nfxcZbxi4IRoNQYlm5 9R8AEQEAAcLAZQQYAQoADwUCU7PEDAIbDAUJBaOagAAKCRCDGMOVW6sif7FRB/4k9y/GaGqU fcJiXdQHRAKHCUvbKMFgeEDHOg33qx+POS2Ah85/PXVa2jYBldCZDmYc+zl48aEMd163a7s3 0gJaB7CYElwxlKUk6c+5gwoYIJuJJzSzW0JzSD5ch7RIRxbfxrKdsiHrUW8AeduZWzlK6VaW RmWILgLmxfLdhEVFWxbr99GSeVFZaZwn6tl/8CvBcgYoARvJvl0V5zS1akQfEISYkwL9EfUI W44EOHranL5qUXkedXBYp6fRsooGrIimfwYxaC8FbXhk3FMgMjDMRiVq4POHo1iGeYETsUrL NM6184E25gPVtX2fb3RhM8Xh6BkwCZ6ZYbQ+AcD4F/cKwsB8BBgBCgAmAhsMFiEE6YzzxOac w80OV51VgxjDlVurIn8FAllgwtgFCQ0xzMwACgkQgxjDlVurIn9OqAf9FAcKWS95wTTbraXA qg/+bQyHgjlMtGCgkmfxLsbUGeqiFgmSIuoDrF7q6sYPs6p00CXXZRuuNZt0lX7O95re8mgz gxm5iJisZpdbHMVepYlw/AxT2wCHwxGCEe64Lm+A9vjlOd+3D3/6fSLwZ9WFCE6p6lQZ1CDg 09xe+JKSgC+KDqmn0tzGKyfSCuhRAq3XkZyxL1hxBaDeP0eeKlzoy7jXodf3wVvXXc0cmpza B5McuRHK4EU6jIioHo30YqPM4AjPHGxV2X1N6/Aayungzj9EXNZtKCxs6dsTvjniWa5VkZ9F 4SOdSbxEen1DZRYpeWnd7GVmO86n+5USkKCXPg== Message-ID: <28c7430b-fb7c-6472-5c1b-fa3ff63a9e73@FreeBSD.org> Date: Wed, 22 May 2019 11:19:34 -0400 User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20190520164202.GA2130@spy> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 2D4718A47E X-Spamd-Bar: ------ Authentication-Results: mx1.freebsd.org; dkim=pass header.d=gmail.com header.s=20161025 header.b=niE/zW7k; spf=pass (mx1.freebsd.org: domain of mavbsd@gmail.com designates 2607:f8b0:4864:20::c30 as permitted sender) smtp.mailfrom=mavbsd@gmail.com X-Spamd-Result: default: False [-6.15 / 15.00]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; R_DKIM_ALLOW(-0.20)[gmail.com:s=20161025]; NEURAL_HAM_MEDIUM(-1.00)[-1.000,0]; FROM_HAS_DN(0.00)[]; RCPT_COUNT_THREE(0.00)[4]; R_SPF_ALLOW(-0.20)[+ip6:2607:f8b0:4000::/36]; TO_MATCH_ENVRCPT_ALL(0.00)[]; MIME_GOOD(-0.10)[text/plain]; RCVD_TLS_LAST(0.00)[]; DMARC_NA(0.00)[FreeBSD.org]; TO_DN_SOME(0.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000,0]; RCVD_COUNT_THREE(0.00)[3]; IP_SCORE(-2.99)[ip: (-9.36), ipnet: 2607:f8b0::/32(-3.26), asn: 15169(-2.27), country: US(-0.06)]; DKIM_TRACE(0.00)[gmail.com:+]; MX_GOOD(-0.01)[cached: alt3.gmail-smtp-in.l.google.com]; RCVD_IN_DNSWL_NONE(0.00)[0.3.c.0.0.0.0.0.0.0.0.0.0.0.0.0.0.2.0.0.4.6.8.4.0.b.8.f.7.0.6.2.list.dnswl.org : 127.0.5.0]; NEURAL_HAM_SHORT(-0.95)[-0.949,0]; FORGED_SENDER(0.30)[mav@FreeBSD.org,mavbsd@gmail.com]; MIME_TRACE(0.00)[0:+]; FREEMAIL_ENVFROM(0.00)[gmail.com]; ASN(0.00)[asn:15169, ipnet:2607:f8b0::/32, country:US]; FROM_NEQ_ENVFROM(0.00)[mav@FreeBSD.org,mavbsd@gmail.com]; MID_RHS_MATCH_FROM(0.00)[] X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 22 May 2019 15:19:41 -0000 On 20.05.2019 12:42, Mark Johnston wrote: > On Mon, May 20, 2019 at 07:05:07PM +0300, Lev Serebryakov wrote: >> >> I'm looking at last commit to >> 'sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c' (r345200) and >> have another question. >> >> Here are such code: >> >> 4960 /* >> 4961 * Kick off asynchronous kmem_reap()'s of all our caches. >> 4962 */ >> 4963 arc_kmem_reap_soon(); >> 4964 >> 4965 /* >> 4966 * Wait at least arc_kmem_cache_reap_retry_ms between >> 4967 * arc_kmem_reap_soon() calls. Without this check it is >> possible to >> 4968 * end up in a situation where we spend lots of time reaping >> 4969 * caches, while we're near arc_c_min. Waiting here also >> gives the >> 4970 * subsequent free memory check a chance of finding that the >> 4971 * asynchronous reap has already freed enough memory, and >> we don't >> 4972 * need to call arc_reduce_target_size(). >> 4973 */ >> 4974 delay((hz * arc_kmem_cache_reap_retry_ms + 999) / 1000); >> 4975 >> >> But looks like `arc_kmem_reap_soon()` is synchronous on FreeBSD! So, >> this `delay()` looks very wrong. Am I right? Why is it wrong? >> Looks like it should be `#ifdef illumos`. > > See also r338142, which I believe was reverted by the update. My r345200 indeed reverted that value, but I don't see a problem there. When OS need more RAM, pagedaemon will drain UMA caches by itself. I don't see a point in re-draining UMA caches in a tight loop without delay. If caches are not sufficient to sustain one second of workload, then usefulness of such caches is not very clear and shrinking ARC to free some space may be a right move. Also making ZFS drain its caches more active then anything else in a system looks unfair to me. -- Alexander Motin