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imf22.hostedemail.com; dkim=none; dmarc=none; spf=pass (imf22.hostedemail.com: domain of shikemeng@huaweicloud.com designates 45.249.212.51 as permitted sender) smtp.mailfrom=shikemeng@huaweicloud.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1712134221; a=rsa-sha256; cv=none; b=M02t+74OCDNwihx1kFLQiAHDQl2Vu7mz682RiBsm81r2hzNPplIpquG8rN46mjdmPu2BSF Rz643B7WZ+Pqy6RXzx0POEl8yOakVDJnkEe45klwqx34Whtjdvw+hFYEviKsldsxnXzb0b MCNs7+3JBhQSiRcNIrtSq5EJroGjHFQ= Received: from mail.maildlp.com (unknown [172.19.163.235]) by dggsgout11.his.huawei.com (SkyGuard) with ESMTP id 4V8djw2xjFz4f3mVZ for ; Wed, 3 Apr 2024 16:50:12 +0800 (CST) Received: from mail02.huawei.com (unknown [10.116.40.112]) by mail.maildlp.com (Postfix) with ESMTP id 9F9C61A0568 for ; Wed, 3 Apr 2024 16:50:16 +0800 (CST) Received: from [10.174.178.129] (unknown [10.174.178.129]) by APP1 (Coremail) with SMTP id cCh0CgD3Ew1HGA1mt0KtIw--.56654S2; Wed, 03 Apr 2024 16:50:16 +0800 (CST) Subject: Re: [PATCH 6/6] writeback: remove unneeded GDTC_INIT_NO_WB To: Jan Kara Cc: Tejun Heo , akpm@linux-foundation.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, willy@infradead.org, bfoster@redhat.com, dsterba@suse.com, mjguzik@gmail.com, dhowells@redhat.com, peterz@infradead.org References: <20240320110222.6564-1-shikemeng@huaweicloud.com> <20240320110222.6564-7-shikemeng@huaweicloud.com> <20240327093309.ejuzjus2zcixb4qt@quack3> <20240402135306.kluke2jjcmh5f4ei@quack3> From: Kemeng Shi Message-ID: <50663bca-3851-42bb-ef1d-5fee8fc7b9b6@huaweicloud.com> Date: Wed, 3 Apr 2024 16:50:15 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.5.0 MIME-Version: 1.0 In-Reply-To: <20240402135306.kluke2jjcmh5f4ei@quack3> Content-Type: text/plain; charset=gbk Content-Transfer-Encoding: 7bit X-CM-TRANSID:cCh0CgD3Ew1HGA1mt0KtIw--.56654S2 X-Coremail-Antispam: 1UD129KBjvJXoWxAw47Zw13Cw4fAw18Cr45KFg_yoW5ZFWfpF W3Xa1DKay5Ja4SqrnIgwn7Xa1rKrZ7t347X3s0kw4UArs5Krn7Krnrta1rCF17Ar1xXw1j vFW3tas7Za1UCFJanT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUvFb4IE77IF4wAFF20E14v26r4j6ryUM7CY07I20VC2zVCF04k2 6cxKx2IYs7xG6rWj6s0DM7CIcVAFz4kK6r1j6r18M28lY4IEw2IIxxk0rwA2F7IY1VAKz4 vEj48ve4kI8wA2z4x0Y4vE2Ix0cI8IcVAFwI0_Ar0_tr1l84ACjcxK6xIIjxv20xvEc7Cj xVAFwI0_Gr1j6F4UJwA2z4x0Y4vEx4A2jsIE14v26rxl6s0DM28EF7xvwVC2z280aVCY1x 0267AKxVW0oVCq3wAS0I0E0xvYzxvE52x082IY62kv0487Mc02F40EFcxC0VAKzVAqx4xG 6I80ewAv7VC0I7IYx2IY67AKxVWUGVWUXwAv7VC2z280aVAFwI0_Jr0_Gr1lOx8S6xCaFV Cjc4AY6r1j6r4UM4x0Y48IcVAKI48JM4IIrI8v6xkF7I0E8cxan2IY04v7Mxk0xIA0c2IE e2xFo4CEbIxvr21l42xK82IYc2Ij64vIr41l4I8I3I0E4IkC6x0Yz7v_Jr0_Gr1lx2IqxV Aqx4xG67AKxVWUJVWUGwC20s026x8GjcxK67AKxVWUGVWUWwC2zVAF1VAY17CE14v26r1q 6r43MIIYrxkI7VAKI48JMIIF0xvE2Ix0cI8IcVAFwI0_Jr0_JF4lIxAIcVC0I7IYx2IY6x kF7I0E14v26r4j6F4UMIIF0xvE42xK8VAvwI8IcIk0rVW8JVW3JwCI42IY6I8E87Iv67AK xVWUJVW8JwCI42IY6I8E87Iv6xkF7I0E14v26r4j6r4UJbIYCTnIWIevJa73UjIFyTuYvj xUOyCJDUUUU X-CM-SenderInfo: 5vklyvpphqwq5kxd4v5lfo033gof0z/ X-Rspamd-Queue-Id: DA653C0010 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: s6kwabigkd133dn5tnxat99im5qpmbgf X-HE-Tag: 1712134220-966927 X-HE-Meta: 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: on 4/2/2024 9:53 PM, Jan Kara wrote: > On Thu 28-03-24 09:49:59, Kemeng Shi wrote: >> on 3/27/2024 5:33 PM, Jan Kara wrote: >>> On Thu 21-03-24 15:12:21, Kemeng Shi wrote: >>>> >>>> >>>> on 3/20/2024 11:15 PM, Tejun Heo wrote: >>>>> Hello, >>>>> >>>>> On Wed, Mar 20, 2024 at 07:02:22PM +0800, Kemeng Shi wrote: >>>>>> We never use gdtc->dom set with GDTC_INIT_NO_WB, just remove unneeded >>>>>> GDTC_INIT_NO_WB >>>>>> >>>>>> Signed-off-by: Kemeng Shi >>>>> ... >>>>>> void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty) >>>>>> { >>>>>> - struct dirty_throttle_control gdtc = { GDTC_INIT_NO_WB }; >>>>>> + struct dirty_throttle_control gdtc = { }; >>>>> >>>>> Even if it's currently not referenced, wouldn't it still be better to always >>>>> guarantee that a dtc's dom is always initialized? I'm not sure what we get >>>>> by removing this. >>>> As we explicitly use GDTC_INIT_NO_WB to set global_wb_domain before >>>> calculating dirty limit with domain_dirty_limits, I intuitively think the >>>> dirty limit calculation in domain_dirty_limits is related to >>>> global_wb_domain when CONFIG_WRITEBACK_CGROUP is enabled while the truth >>>> is not. So this is a little confusing to me. >>> >> Hi Jan, >>> I'm not sure I understand your confusion. domain_dirty_limits() calculates >>> the dirty limit (and background dirty limit) for the dirty_throttle_control >>> passed in. If you pass dtc initialized with GDTC_INIT[_NO_WB], it will >>> compute global dirty limits. If the dtc passed in is initialized with >>> MDTC_INIT() it will compute cgroup specific dirty limits. >> No doubt about this. >>> >>> Now because domain_dirty_limits() does not scale the limits based on each >>> device throughput - that is done only later in __wb_calc_thresh() to avoid> relatively expensive computations when we don't need them - and also >>> because the effective dirty limit (dtc->dom->dirty_limit) is not updated by >>> domain_dirty_limits(), domain_dirty_limits() does not need dtc->dom at all. >> Acutally, here is the thing confusing me. For wb_calc_thresh, we always pass >> dtc initialized with a wb (GDTC_INIT(wb) or MDTC_INIT(wb,..). The dtc >> initialized with _NO_WB is only passed to domain_dirty_limits. However, The >> dom initialized by _NO_WB for domain_dirty_limits is not needed at all. >>> But that is a technical detail of implementation and I don't want this >>> technical detail to be relied on by even more code. >> Yes, I agree with this. So I wonder if it's acceptable to simply define >> GDTC_INIT_NO_WB to empty for now instead of remove defination of >> GDTC_INIT_NO_WB. When implementation of domain_dirty_limits() or any >> other low level function in future using GDTC_INIT(_NO_WB) changes to >> need dtc->domain, we re-define GDTC_INIT_NO_WB to proper value. >> As this only looks confusing to me. I will drop this one in next version >> if you still prefer to keep definatino of GDTC_INIT_NO_WB in the old way. > > Yeah, please keep the code as is for now. I agree this needs some cleanups > but what you suggest is IMHO not an improvement. Sure, will drop this in next version. Thanks, Kemeng > > Honza >