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=-11.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 21B72C433E0 for ; Tue, 14 Jul 2020 06:20:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EE5E5221E7 for ; Tue, 14 Jul 2020 06:20:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725853AbgGNGUx (ORCPT ); Tue, 14 Jul 2020 02:20:53 -0400 Received: from mx2.suse.de ([195.135.220.15]:46292 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725778AbgGNGUx (ORCPT ); Tue, 14 Jul 2020 02:20:53 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 09D74B635; Tue, 14 Jul 2020 06:20:53 +0000 (UTC) Subject: Re: [PATCH] bcache: add a new sysfs interface to disable refill when read miss To: Hannes Reinecke , Guoju Fang Cc: linux-bcache@vger.kernel.org, linux-block@vger.kernel.org References: <1594610902-4428-1-git-send-email-fangguoju@gmail.com> <141fbeaf-8fb6-43fb-56ed-5f8a5a019cc7@suse.de> From: Coly Li Autocrypt: addr=colyli@suse.de; keydata= mQINBFYX6S8BEAC9VSamb2aiMTQREFXK4K/W7nGnAinca7MRuFUD4JqWMJ9FakNRd/E0v30F qvZ2YWpidPjaIxHwu3u9tmLKqS+2vnP0k7PRHXBYbtZEMpy3kCzseNfdrNqwJ54A430BHf2S GMVRVENiScsnh4SnaYjFVvB8SrlhTsgVEXEBBma5Ktgq9YSoy5miatWmZvHLFTQgFMabCz/P j5/xzykrF6yHo0rHZtwzQzF8rriOplAFCECp/t05+OeHHxjSqSI0P/G79Ll+AJYLRRm9til/ K6yz/1hX5xMToIkYrshDJDrUc8DjEpISQQPhG19PzaUf3vFpmnSVYprcWfJWsa2wZyyjRFkf J51S82WfclafNC6N7eRXedpRpG6udUAYOA1YdtlyQRZa84EJvMzW96iSL1Gf+ZGtRuM3k49H 1wiWOjlANiJYSIWyzJjxAd/7Xtiy/s3PRKL9u9y25ftMLFa1IljiDG+mdY7LyAGfvdtIkanr iBpX4gWXd7lNQFLDJMfShfu+CTMCdRzCAQ9hIHPmBeZDJxKq721CyBiGAhRxDN+TYiaG/UWT 7IB7LL4zJrIe/xQ8HhRO+2NvT89o0LxEFKBGg39yjTMIrjbl2ZxY488+56UV4FclubrG+t16 r2KrandM7P5RjR+cuHhkKseim50Qsw0B+Eu33Hjry7YCihmGswARAQABtBhDb2x5IExpIDxj b2x5bGlAc3VzZS5kZT6JAlYEEwEIAEACGyMHCwkIBwMCAQYVCAIJCgsEFgIDAQIeAQIXgBYh BOo+RS/0+Uhgjej60Mc5B5Nrffj8BQJcR84dBQkY++fuAAoJEMc5B5Nrffj8ixcP/3KAKg1X EcoW4u/0z+Ton5rCyb/NpAww8MuRjNW82UBUac7yCi1y3OW7NtLjuBLw5SaVG5AArb7IF3U0 qTOobqfl5XHsT0o5wFHZaKUrnHb6y7V3SplsJWfkP3JmOooJsQB3z3K96ZTkFelsNb0ZaBRu gV+LA4MomhQ+D3BCDR1it1OX/tpvm2uaDF6s/8uFtcDEM9eQeqATN/QAJ49nvU/I8zDSY9rc 0x9mP0x+gH4RccbnoPu/rUG6Fm1ZpLrbb6NpaYBBJ/V1BC4lIOjnd24bsoQrQmnJn9dSr60X 1MY60XDszIyzRw7vbJcUn6ZzPNFDxFFT9diIb+wBp+DD8ZlD/hnVpl4f921ZbvfOSsXAJrKB 1hGY17FPwelp1sPcK2mDT+pfHEMV+OQdZzD2OCKtza/5IYismJJm3oVUYMogb5vDNAw9X2aP XgwUuG+FDEFPamFMUwIfzYHcePfqf0mMsaeSgtA/xTxzx/0MLjUJHl46Bc0uKDhv7QUyGz0j Ywgr2mHTvG+NWQ/mDeHNGkcnsnp3IY7koDHnN2xMFXzY4bn9m8ctqKo2roqjCzoxD/njoAhf KBzdybLHATqJG/yiZSbCxDA1n/J4FzPyZ0rNHUAJ/QndmmVspE9syFpFCKigvvyrzm016+k+ FJ59Q6RG4MSy/+J565Xj+DNY3/dCuQINBFYX6S8BEADZP+2cl4DRFaSaBms08W8/smc5T2CO YhAoygZn71rB7Djml2ZdvrLRjR8Qbn0Q/2L2gGUVc63pJnbrjlXSx2LfAFE0SlfYIJ11aFdF 9w7RvqWByQjDJor3Z0fWvPExplNgMvxpD0U0QrVT5dIGTx9hadejCl/ug09Lr6MPQn+a4+qs aRWwgCSHaIuDkH3zI1MJXiqXXFKUzJ/Fyx6R72rqiMPHH2nfwmMu6wOXAXb7+sXjZz5Po9GJ g2OcEc+rpUtKUJGyeQsnCDxUcqJXZDBi/GnhPCcraQuqiQ7EGWuJfjk51vaI/rW4bZkA9yEP B9rBYngbz7cQymUsfxuTT8OSlhxjP3l4ZIZFKIhDaQeZMj8pumBfEVUyiF6KVSfgfNQ/5PpM R4/pmGbRqrAAElhrRPbKQnCkGWDr8zG+AjN1KF6rHaFgAIO7TtZ+F28jq4reLkur0N5tQFww wFwxzROdeLHuZjL7eEtcnNnzSkXHczLkV4kQ3+vr/7Gm65mQfnVpg6JpwpVrbDYQeOFlxZ8+ GERY5Dag4KgKa/4cSZX2x/5+KkQx9wHwackw5gDCvAdZ+Q81nm6tRxEYBBiVDQZYqO73stgT ZyrkxykUbQIy8PI+g7XMDCMnPiDncQqgf96KR3cvw4wN8QrgA6xRo8xOc2C3X7jTMQUytCz9 0MyV1QARAQABiQI8BBgBCAAmAhsMFiEE6j5FL/T5SGCN6PrQxzkHk2t9+PwFAlxHziAFCRj7 5/EACgkQxzkHk2t9+PxgfA//cH5R1DvpJPwraTAl24SUcG9EWe+NXyqveApe05nk15zEuxxd e4zFEjo+xYZilSveLqYHrm/amvQhsQ6JLU+8N60DZHVcXbw1Eb8CEjM5oXdbcJpXh1/1BEwl 4phsQMkxOTns51bGDhTQkv4lsZKvNByB9NiiMkT43EOx14rjkhHw3rnqoI7ogu8OO7XWfKcL CbchjJ8t3c2XK1MUe056yPpNAT2XPNF2EEBPG2Y2F4vLgEbPv1EtpGUS1+JvmK3APxjXUl5z 6xrxCQDWM5AAtGfM/IswVjbZYSJYyH4BQKrShzMb0rWUjkpXvvjsjt8rEXpZEYJgX9jvCoxt oqjCKiVLpwje9WkEe9O9VxljmPvxAhVqJjX62S+TGp93iD+mvpCoHo3+CcvyRcilz+Ko8lfO hS9tYT0HDUiDLvpUyH1AR2xW9RGDevGfwGTpF0K6cLouqyZNdhlmNciX48tFUGjakRFsxRmX K0Jx4CEZubakJe+894sX6pvNFiI7qUUdB882i5GR3v9ijVPhaMr8oGuJ3kvwBIA8lvRBGVGn 9xvzkQ8Prpbqh30I4NMp8MjFdkwCN6znBKPHdjNTwE5PRZH0S9J0o67IEIvHfH0eAWAsgpTz +jwc7VKH7vkvgscUhq/v1/PEWCAqh9UHy7R/jiUxwzw/288OpgO+i+2l11Y= Message-ID: <7f52be25-3bcd-17b9-b9a7-219820d71c17@suse.de> Date: Tue, 14 Jul 2020 14:20:45 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <141fbeaf-8fb6-43fb-56ed-5f8a5a019cc7@suse.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-bcache-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-bcache@vger.kernel.org On 2020/7/14 13:57, Hannes Reinecke wrote: > On 7/13/20 5:28 AM, Guoju Fang wrote: >> When read cache miss, backing device will be read first, and then refill >> the cache device. But under some scenarios there are large number of new >> reads and rarely hit, so it's necessary to disable the refill when read >> miss to save space for writes. >> >> This patch add a new config called refill_on_miss_disabled which is >> not set >> by default. Bcache user can set it by sysfs interface and then the bcache >> device will not refill when read cache miss. >> >> Signed-off-by: Guoju Fang >> --- >>   drivers/md/bcache/bcache.h  | 1 + >>   drivers/md/bcache/request.c | 2 ++ >>   drivers/md/bcache/super.c   | 1 + >>   drivers/md/bcache/sysfs.c   | 5 +++++ >>   4 files changed, 9 insertions(+) >> >> diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h >> index 221e0191b687..3a19ee6de3a7 100644 >> --- a/drivers/md/bcache/bcache.h >> +++ b/drivers/md/bcache/bcache.h >> @@ -730,6 +730,7 @@ struct cache_set { >>       unsigned int        shrinker_disabled:1; >>       unsigned int        copy_gc_enabled:1; >>       unsigned int        idle_max_writeback_rate_enabled:1; >> +    unsigned int        refill_on_miss_disabled:1; >>     #define BUCKET_HASH_BITS    12 >>       struct hlist_head    bucket_hash[1 << BUCKET_HASH_BITS]; >> diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c >> index 7acf024e99f3..4bfa0e0b4b3f 100644 >> --- a/drivers/md/bcache/request.c >> +++ b/drivers/md/bcache/request.c >> @@ -378,6 +378,8 @@ static bool check_should_bypass(struct cached_dev >> *dc, struct bio *bio) >>            op_is_write(bio_op(bio)))) >>           goto skip; >>   +    if (c->refill_on_miss_disabled && !op_is_write(bio_op(bio))) >> +        goto skip; >>       /* >>        * If the bio is for read-ahead or background IO, bypass it or >>        * not depends on the following situations, >> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c >> index 2014016f9a60..c1e9bfec1267 100644 >> --- a/drivers/md/bcache/super.c >> +++ b/drivers/md/bcache/super.c >> @@ -1862,6 +1862,7 @@ struct cache_set *bch_cache_set_alloc(struct >> cache_sb *sb) >>       c->congested_write_threshold_us    = 20000; >>       c->error_limit    = DEFAULT_IO_ERROR_LIMIT; >>       c->idle_max_writeback_rate_enabled = 1; >> +    c->refill_on_miss_disabled = 0; >>       WARN_ON(test_and_clear_bit(CACHE_SET_IO_DISABLE, &c->flags)); >>         return c; >> diff --git a/drivers/md/bcache/sysfs.c b/drivers/md/bcache/sysfs.c >> index 0dadec5a78f6..178300f401bb 100644 >> --- a/drivers/md/bcache/sysfs.c >> +++ b/drivers/md/bcache/sysfs.c >> @@ -144,6 +144,7 @@ rw_attribute(copy_gc_enabled); >>   rw_attribute(idle_max_writeback_rate); >>   rw_attribute(gc_after_writeback); >>   rw_attribute(size); >> +rw_attribute(refill_on_miss_disabled); >>     static ssize_t bch_snprint_string_list(char *buf, >>                          size_t size, >> @@ -779,6 +780,8 @@ SHOW(__bch_cache_set) >>       if (attr == &sysfs_bset_tree_stats) >>           return bch_bset_print_stats(c, buf); >>   +    sysfs_printf(refill_on_miss_disabled, "%i", >> c->refill_on_miss_disabled); >> + >>       return 0; >>   } >>   SHOW_LOCKED(bch_cache_set) >> @@ -898,6 +901,7 @@ STORE(__bch_cache_set) >>        * set in next chance. >>        */ >>       sysfs_strtoul_clamp(gc_after_writeback, c->gc_after_writeback, >> 0, 1); >> +    sysfs_strtoul(refill_on_miss_disabled, c->refill_on_miss_disabled); >>         return size; >>   } >> @@ -948,6 +952,7 @@ static struct attribute *bch_cache_set_files[] = { >>       &sysfs_congested_read_threshold_us, >>       &sysfs_congested_write_threshold_us, >>       &sysfs_clear_stats, >> +    &sysfs_refill_on_miss_disabled, >>       NULL >>   }; >>   KTYPE(bch_cache_set); >> Hi Hannes, > Please don't call the attribute refill_on_miss_disabled. > This kind of double-negation will always lead to issues; please invert > the meaning and call it 'refill_on_miss'. The original purpose is to implement a "write-only" or "read-around" like cache. Such kind of cache model is desired for heavy write condition, and disable the read-miss-refill may also help to extend the SSD life time. Naming is a challenge here. Becuase "write-only" is not true while read hitting on dirty data on cache device may successfully return, and "read-around" is also not true due to the same reason. We do need help for people to suggest a proper mode for such cache mode, or cache configuration (if we don't want one more cache mode). Thanks. Coly Li