From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 003DDC46470 for ; Tue, 7 Aug 2018 06:34:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A184021A0D for ; Tue, 7 Aug 2018 06:34:49 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A184021A0D Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388632AbeHGIrf (ORCPT ); Tue, 7 Aug 2018 04:47:35 -0400 Received: from mx2.suse.de ([195.135.220.15]:56394 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1733217AbeHGIrf (ORCPT ); Tue, 7 Aug 2018 04:47:35 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 7C255ACEF; Tue, 7 Aug 2018 06:34:44 +0000 (UTC) Subject: Re: [PATCH 1/4] xen/blkback: don't keep persistent grants too long To: =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= Cc: linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org, linux-block@vger.kernel.org, konrad.wilk@oracle.com, axboe@kernel.dk, boris.ostrovsky@oracle.com References: <20180806113403.24728-1-jgross@suse.com> <20180806113403.24728-2-jgross@suse.com> <20180806155852.7jvudjpzzq6fdp33@mac> From: Juergen Gross Openpgp: preference=signencrypt Autocrypt: addr=jgross@suse.com; prefer-encrypt=mutual; keydata= xsBNBFOMcBYBCACgGjqjoGvbEouQZw/ToiBg9W98AlM2QHV+iNHsEs7kxWhKMjrioyspZKOB ycWxw3ie3j9uvg9EOB3aN4xiTv4qbnGiTr3oJhkB1gsb6ToJQZ8uxGq2kaV2KL9650I1SJve dYm8Of8Zd621lSmoKOwlNClALZNew72NjJLEzTalU1OdT7/i1TXkH09XSSI8mEQ/ouNcMvIJ NwQpd369y9bfIhWUiVXEK7MlRgUG6MvIj6Y3Am/BBLUVbDa4+gmzDC9ezlZkTZG2t14zWPvx XP3FAp2pkW0xqG7/377qptDmrk42GlSKN4z76ELnLxussxc7I2hx18NUcbP8+uty4bMxABEB AAHNHkp1ZXJnZW4gR3Jvc3MgPGpncm9zc0BzdXNlLmRlPsLAeQQTAQIAIwUCU4xw6wIbAwcL CQgHAwIBBhUIAgkKCwQWAgMBAh4BAheAAAoJELDendYovxMvi4UH/Ri+OXlObzqMANruTd4N zmVBAZgx1VW6jLc8JZjQuJPSsd/a+bNr3BZeLV6lu4Pf1Yl2Log129EX1KWYiFFvPbIiq5M5 kOXTO8Eas4CaScCvAZ9jCMQCgK3pFqYgirwTgfwnPtxFxO/F3ZcS8jovza5khkSKL9JGq8Nk czDTruQ/oy0WUHdUr9uwEfiD9yPFOGqp4S6cISuzBMvaAiC5YGdUGXuPZKXLpnGSjkZswUzY d9BVSitRL5ldsQCg6GhDoEAeIhUC4SQnT9SOWkoDOSFRXZ+7+WIBGLiWMd+yKDdRG5RyP/8f 3tgGiB6cyuYfPDRGsELGjUaTUq3H2xZgIPfOwE0EU4xwFgEIAMsx+gDjgzAY4H1hPVXgoLK8 B93sTQFN9oC6tsb46VpxyLPfJ3T1A6Z6MVkLoCejKTJ3K9MUsBZhxIJ0hIyvzwI6aYJsnOew cCiCN7FeKJ/oA1RSUemPGUcIJwQuZlTOiY0OcQ5PFkV5YxMUX1F/aTYXROXgTmSaw0aC1Jpo w7Ss1mg4SIP/tR88/d1+HwkJDVW1RSxC1PWzGizwRv8eauImGdpNnseneO2BNWRXTJumAWDD pYxpGSsGHXuZXTPZqOOZpsHtInFyi5KRHSFyk2Xigzvh3b9WqhbgHHHE4PUVw0I5sIQt8hJq 5nH5dPqz4ITtCL9zjiJsExHuHKN3NZsAEQEAAcLAXwQYAQIACQUCU4xwFgIbDAAKCRCw3p3W KL8TL0P4B/9YWver5uD/y/m0KScK2f3Z3mXJhME23vGBbMNlfwbr+meDMrJZ950CuWWnQ+d+ Ahe0w1X7e3wuLVODzjcReQ/v7b4JD3wwHxe+88tgB9byc0NXzlPJWBaWV01yB2/uefVKryAf AHYEd0gCRhx7eESgNBe3+YqWAQawunMlycsqKa09dBDL1PFRosF708ic9346GLHRc6Vj5SRA UTHnQqLetIOXZm3a2eQ1gpQK9MmruO86Vo93p39bS1mqnLLspVrL4rhoyhsOyh0Hd28QCzpJ wKeHTd0MAWAirmewHXWPco8p1Wg+V+5xfZzuQY0f4tQxvOpXpt4gQ1817GQ5/Ed/wsDtBBgB CAAgFiEEhRJncuj2BJSl0Jf3sN6d1ii/Ey8FAlrd8NACGwIAgQkQsN6d1ii/Ey92IAQZFggA HRYhBFMtsHpB9jjzHji4HoBcYbtP2GO+BQJa3fDQAAoJEIBcYbtP2GO+TYsA/30H/0V6cr/W V+J/FCayg6uNtm3MJLo4rE+o4sdpjjsGAQCooqffpgA+luTT13YZNV62hAnCLKXH9n3+ZAgJ RtAyDWk1B/0SMDVs1wxufMkKC3Q/1D3BYIvBlrTVKdBYXPxngcRoqV2J77lscEvkLNUGsu/z W2pf7+P3mWWlrPMJdlbax00vevyBeqtqNKjHstHatgMZ2W0CFC4hJ3YEetuRBURYPiGzuJXU pAd7a7BdsqWC4o+GTm5tnGrCyD+4gfDSpkOT53S/GNO07YkPkm/8J4OBoFfgSaCnQ1izwgJQ jIpcG2fPCI2/hxf2oqXPYbKr1v4Z1wthmoyUgGN0LPTIm+B5vdY82wI5qe9uN6UOGyTH2B3p hRQUWqCwu2sqkI3LLbTdrnyDZaixT2T0f4tyF5Lfs+Ha8xVMhIyzNb1byDI5FKCb Message-ID: Date: Tue, 7 Aug 2018 08:34:43 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20180806155852.7jvudjpzzq6fdp33@mac> Content-Type: text/plain; charset=utf-8 Content-Language: de-DE Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/08/18 17:58, Roger Pau Monné wrote: > On Mon, Aug 06, 2018 at 01:33:59PM +0200, Juergen Gross wrote: >> Persistent grants are allocated until a threshold per ring is being >> reached. Those grants won't be freed until the ring is being destroyed >> meaning there will be resources kept busy which might no longer be >> used. >> >> Instead of freeing only persistent grants until the threshold is >> reached add a timestamp and remove all persistent grants not having >> been in use for a minute. >> >> Signed-off-by: Juergen Gross >> --- >> drivers/block/xen-blkback/blkback.c | 77 +++++++++++++++++++++++-------------- >> drivers/block/xen-blkback/common.h | 1 + >> 2 files changed, 50 insertions(+), 28 deletions(-) > > You should document this new parameter in > Documentation/ABI/testing/sysfs-driver-xen-blkback. Yes. > >> >> diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c >> index b55b245e8052..485e3ecab144 100644 >> --- a/drivers/block/xen-blkback/blkback.c >> +++ b/drivers/block/xen-blkback/blkback.c >> @@ -84,6 +84,18 @@ MODULE_PARM_DESC(max_persistent_grants, >> "Maximum number of grants to map persistently"); >> >> /* >> + * How long a persistent grant is allowed to remain allocated without being in >> + * use. The time is in seconds, 0 means indefinitely long. >> + */ >> + >> +unsigned int xen_blkif_pgrant_timeout = 60; >> +module_param_named(persistent_grant_unused_seconds, xen_blkif_pgrant_timeout, >> + uint, 0644); >> +MODULE_PARM_DESC(persistent_grant_unused_seconds, >> + "Time in seconds an unused persistent grant is allowed to " >> + "remain allocated. Default is 60, 0 means unlimited."); >> + >> +/* >> * Maximum number of rings/queues blkback supports, allow as many queues as there >> * are CPUs if user has not specified a value. >> */ >> @@ -123,6 +135,13 @@ module_param(log_stats, int, 0644); >> /* Number of free pages to remove on each call to gnttab_free_pages */ >> #define NUM_BATCH_FREE_PAGES 10 >> >> +static inline bool persistent_gnt_timeout(struct persistent_gnt *persistent_gnt) >> +{ >> + return xen_blkif_pgrant_timeout && >> + (jiffies - persistent_gnt->last_used >= >> + HZ * xen_blkif_pgrant_timeout); >> +} >> + >> static inline int get_free_page(struct xen_blkif_ring *ring, struct page **page) >> { >> unsigned long flags; >> @@ -278,6 +297,7 @@ static void put_persistent_gnt(struct xen_blkif_ring *ring, >> { >> if(!test_bit(PERSISTENT_GNT_ACTIVE, persistent_gnt->flags)) >> pr_alert_ratelimited("freeing a grant already unused\n"); >> + persistent_gnt->last_used = jiffies; >> set_bit(PERSISTENT_GNT_WAS_ACTIVE, persistent_gnt->flags); >> clear_bit(PERSISTENT_GNT_ACTIVE, persistent_gnt->flags); >> atomic_dec(&ring->persistent_gnt_in_use); >> @@ -374,23 +394,23 @@ static void purge_persistent_gnt(struct xen_blkif_ring *ring) >> bool scan_used = false, clean_used = false; >> struct rb_root *root; >> >> - if (ring->persistent_gnt_c < xen_blkif_max_pgrants || >> - (ring->persistent_gnt_c == xen_blkif_max_pgrants && >> - !ring->blkif->vbd.overflow_max_grants)) { >> - goto out; >> - } >> - >> if (work_busy(&ring->persistent_purge_work)) { >> pr_alert_ratelimited("Scheduled work from previous purge is still busy, cannot purge list\n"); >> goto out; >> } >> >> - num_clean = (xen_blkif_max_pgrants / 100) * LRU_PERCENT_CLEAN; >> - num_clean = ring->persistent_gnt_c - xen_blkif_max_pgrants + num_clean; >> - num_clean = min(ring->persistent_gnt_c, num_clean); >> - if ((num_clean == 0) || >> - (num_clean > (ring->persistent_gnt_c - atomic_read(&ring->persistent_gnt_in_use)))) >> - goto out; >> + if (ring->persistent_gnt_c < xen_blkif_max_pgrants || >> + (ring->persistent_gnt_c == xen_blkif_max_pgrants && >> + !ring->blkif->vbd.overflow_max_grants)) { >> + num_clean = 0; >> + } else { >> + num_clean = (xen_blkif_max_pgrants / 100) * LRU_PERCENT_CLEAN; >> + num_clean = ring->persistent_gnt_c - xen_blkif_max_pgrants + >> + num_clean; >> + num_clean = min(ring->persistent_gnt_c, num_clean); >> + pr_debug("Going to purge at least %u persistent grants\n", >> + num_clean); >> + } >> >> /* >> * At this point, we can assure that there will be no calls >> @@ -401,9 +421,7 @@ static void purge_persistent_gnt(struct xen_blkif_ring *ring) >> * number of grants. >> */ >> >> - total = num_clean; >> - >> - pr_debug("Going to purge %u persistent grants\n", num_clean); >> + total = 0; >> >> BUG_ON(!list_empty(&ring->persistent_purge_list)); >> root = &ring->persistent_gnts; >> @@ -419,39 +437,42 @@ static void purge_persistent_gnt(struct xen_blkif_ring *ring) >> >> if (test_bit(PERSISTENT_GNT_ACTIVE, persistent_gnt->flags)) >> continue; >> - if (!scan_used && >> + if (!scan_used && !persistent_gnt_timeout(persistent_gnt) && >> (test_bit(PERSISTENT_GNT_WAS_ACTIVE, persistent_gnt->flags))) > > If you store the jiffies of the time when the grant was last used it > seems like we could get rid of the PERSISTENT_GNT_WAS_ACTIVE flag and > instead use the per-grant jiffies and the jiffies from the last scan > in order to decide which grants to remove? True. This might make the control flow a little bit easier to understand. Juergen