From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx1.redhat.com (ext-mx10.extmail.prod.ext.phx2.redhat.com [10.5.110.39]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2459185576 for ; Fri, 19 Oct 2018 13:17:00 +0000 (UTC) Received: from mail.service4.ru (mail.service4.ru [195.201.68.178]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 0AA0A9D434 for ; Fri, 19 Oct 2018 13:16:58 +0000 (UTC) Received: from mail.service4.ru (localhost [127.0.0.1]) by mail.service4.ru (Postfix) with ESMTP id C2D9E407FB for ; Fri, 19 Oct 2018 16:16:56 +0300 (MSK) Received: from mail.service4.ru ([127.0.0.1]) by mail.service4.ru (mail.service4.ru [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id OLy5YmxzKOmo for ; Fri, 19 Oct 2018 16:16:56 +0300 (MSK) Received: from ilia (128-68-196-240.broadband.corbina.ru [128.68.196.240]) by mail.service4.ru (Postfix) with ESMTPSA id ED1854036E for ; Fri, 19 Oct 2018 16:16:55 +0300 (MSK) References: <06b65c62-8ca2-0d29-b98d-1a1585141f81@redhat.com> <8ecbd3c8-4819-9ff2-40b1-315e6ae03c97@izyk.ru> <36f0f734-c49f-eaf9-7ff5-8aedfd7345b3@redhat.com> <707aafdc-cfd2-3bdd-13bb-1bfdc08c6ad9@assyoma.it> From: Ilia Zykov Message-ID: Date: Fri, 19 Oct 2018 16:16:54 +0300 MIME-Version: 1.0 In-Reply-To: Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha-256; boundary="------------ms000108030803010704000704" Subject: Re: [linux-lvm] Why doesn't the lvmcache support the discard (trim) command? Reply-To: LVM general discussion and development List-Id: LVM general discussion and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , List-Id: To: LVM general discussion and development This is a cryptographically signed message in MIME format. --------------ms000108030803010704000704 Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 19.10.2018 16:08, Zdenek Kabelac wrote: > Dne 19. 10. 18 v 14:45 Gionatan Danti napsal(a): >> On 19/10/2018 12:58, Zdenek Kabelac wrote: >>> Hi >>> >>> Writecache simply doesn't care about caching your reads at all. >>> Your RAM with it's page caching mechanism keeps read data as long as >>> there is free RAM for this - the less RAM goes to page cache - less >>> read operations remains cached. >> >> Hi, does it mean that to have *both* fast write cache *and* read cache= >> one should use a dm-writeback target + a dm-cache writethrough target >> (possibly pointing to different devices)? >> >> Can you quantify/explain why and how faster is dm-writeback for heavy >> write workload? >=20 >=20 >=20 > Hi >=20 > It's rather about different workload takes benefit from different > caching approaches. >=20 > If your system is heavy on writes -=C2=A0 dm-writecache is what you wan= t, > if you mostly reads - dm-cache will win. >=20 > That's why there is=C2=A0 dmstats to also help identify hotspots and ov= eral > logic. > There is nothing to win always in all cases - so ATM 2 different target= s > are provided -=C2=A0 NVDIMMs already seems to change game a lot... >=20 > dm-writecache could be seen as 'extension' of your page-cache to held > longer list of dirty-pages... >=20 > Zdenek Sorry, but I don't understand too. What be if reboot happens between data= writes from the fast cache to the slow device? After reboot what data wi= ll be reads? A new data from the fast cache or an old from the slow devic= e? And what data will be read 'dd if=3D/dev/cached iflag=3Ddirect'?=20 Thanks. --------------ms000108030803010704000704 Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="smime.p7s" Content-Description: S/MIME Cryptographic Signature MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCC CxIwggUkMIIEDKADAgECAhEA73vYhU4F6WFKdCcfBcRrKjANBgkqhkiG9w0BAQsFADCBlzEL MAkGA1UEBhMCR0IxGzAZBgNVBAgTEkdyZWF0ZXIgTWFuY2hlc3RlcjEQMA4GA1UEBxMHU2Fs Zm9yZDEaMBgGA1UEChMRQ09NT0RPIENBIExpbWl0ZWQxPTA7BgNVBAMTNENPTU9ETyBSU0Eg Q2xpZW50IEF1dGhlbnRpY2F0aW9uIGFuZCBTZWN1cmUgRW1haWwgQ0EwHhcNMTgwNDIwMDAw MDAwWhcNMTkwNDIwMjM1OTU5WjAdMRswGQYJKoZIhvcNAQkBFgxtYWlsQGl6eWsucnUwggEi MA0GCSqGSIb3DQEBAQUAA4IBDwAwggEKAoIBAQCu+RV0CiXSbZX5GWUw5M4PhdbkC4p8rAXp i1O/h8jnk1uJ9MVJMDrt5waZ13kGrs445Vv3ffBsLCTHFcrOTBRgMkMtfYu0i2rSqmT6VgK+ 3oU1YgNueCaAsFVYoV5zHr2xIqW8jOZXEbrrRkTjMnNHcfSTOoXBHRzCAZ4F39/InKIWrtji 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