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WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.5.0 MIME-Version: 1.0 In-Reply-To: <20240327093309.ejuzjus2zcixb4qt@quack3> Content-Type: text/plain; charset=gbk Content-Transfer-Encoding: 7bit X-CM-TRANSID:gCh0CgDnOWzHzARmkrC_IQ--.19172S2 X-Coremail-Antispam: 1UD129KBjvJXoWxCFyUGry8Jry8Cw1kurW8tFb_yoW5trW3pF W3Wa1DK3W5Ja4SvrnxKwn7X3Z8KrZ7try7X3s0kw4DZrs5Grn7Krn2qa1ruF12yr1xXr1r ZFWSqas7Za1UCFJanT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUvIb4IE77IF4wAFF20E14v26r4j6ryUM7CY07I20VC2zVCF04k2 6cxKx2IYs7xG6rWj6s0DM7CIcVAFz4kK6r1j6r18M28lY4IEw2IIxxk0rwA2F7IY1VAKz4 vEj48ve4kI8wA2z4x0Y4vE2Ix0cI8IcVAFwI0_tr0E3s1l84ACjcxK6xIIjxv20xvEc7Cj xVAFwI0_Gr1j6F4UJwA2z4x0Y4vEx4A2jsIE14v26rxl6s0DM28EF7xvwVC2z280aVCY1x 0267AKxVW0oVCq3wAS0I0E0xvYzxvE52x082IY62kv0487Mc02F40EFcxC0VAKzVAqx4xG 6I80ewAv7VC0I7IYx2IY67AKxVWUJVWUGwAv7VC2z280aVAFwI0_Jr0_Gr1lOx8S6xCaFV Cjc4AY6r1j6r4UM4x0Y48IcVAKI48JM4IIrI8v6xkF7I0E8cxan2IY04v7Mxk0xIA0c2IE e2xFo4CEbIxvr21l42xK82IYc2Ij64vIr41l4I8I3I0E4IkC6x0Yz7v_Jr0_Gr1lx2IqxV Aqx4xG67AKxVWUJVWUGwC20s026x8GjcxK67AKxVWUGVWUWwC2zVAF1VAY17CE14v26r1q 6r43MIIYrxkI7VAKI48JMIIF0xvE2Ix0cI8IcVAFwI0_Jr0_JF4lIxAIcVC0I7IYx2IY6x kF7I0E14v26r4j6F4UMIIF0xvE42xK8VAvwI8IcIk0rVWrZr1j6s0DMIIF0xvEx4A2jsIE 14v26r1j6r4UMIIF0xvEx4A2jsIEc7CjxVAFwI0_Gr0_Gr1UYxBIdaVFxhVjvjDU0xZFpf 9x07UWE__UUUUU= X-CM-SenderInfo: 5vklyvpphqwq5kxd4v5lfo033gof0z/ X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: E1862160018 X-Stat-Signature: 3xuosa85bapue6dapsr3xoy4au9bdtjn X-Rspam-User: X-HE-Tag: 1711590606-14239 X-HE-Meta: U2FsdGVkX1+YOvVP8z0q7b4Se9hr53NwFjFivt7c/yJPEfg5Rno9ZSD/p8fYEYLd2JIuZUZUzyjGoN3bEt/xzVtrt/wnvqewmeQoD56dm+xcq5JtJgN5ETrnyzs+kA/bWUHvQHb3gv/YhBXCFqhfELGrT/5Ol3kMgCXFm+StVnyAFppo9a3fG8Utqd/d1J4LBoeMV5Sc8lgcaFTDMVO052b24gdxH7gMgDovEMzUqiuUGy0EC53FHnpJWhZ+7ZYfR50emiChsyNaWIV3HmqoaQDIbBf/9SujZaMwS5H0inF9hinBll7nkzlBceZQYymoJMJMavHh+CVL7yXJ1ih0XJlDjlfuis3f0NICyrdPsuEdgNsJGBEwC15N6E8MRChxn/FZs37AAiNGJSucig/qcwWVaDH4lNGDM+y6w1xRdDDhw0OLxVeUlfV/M/o9ltMufYuzoJT9fNOYPUXz9HOKhjrmtKHNRa0NH/avLznX/ZbefCiufN8of2WA8GhGUN1ELDXnN2n+sVHPvcKZHfR/+P3GW1WpKYjeqrKYypg2bMQ90qFANWC3h10n+JdNTFDo5YCbhK2GgJ0jy878iChNPcsuigmrIHY/PN9X73yZnrvQWDfBNFN6YGrJ8DUiDLgQSUMsH7yoBXZoUzpAngkoDHfTb5AZVjawq4iwzVdQki0akFKiFMOB7ifKLTcOEoiK3tTbmmFcy5h3RHnyQIPMRQmiYQbYuonLcMg/s2beB3AWwHLacDmdljfPWc/y8O5dIQwFPCNxoIiGd47O5Gl+vK4rBHWGLCWvQKkkEjJ86uaA2+8G5X/hb2jKGy6Ki7YOYn4Em0Ivto59xjvgAtvIivUdI0kiyXs7d2xagU+wK0oNdAH4wumV9rT1fJaZwmZ6+2ihOtf01rs3eTK+5fH6lap9r6urAXPou8m1Rh4svSCJqtBLHD2xhKPwSE4EJa4eMk0Jm8Ul9kZAw2yv/Nl 720C1kpT pbDv1KGxYoKFkPfgiTjfK1ffHUONY5g6nnXLyghUVELpg7yeevO+wlVqnxhJiEOHe4932olV4YcOp9k+CGjEO6sB4wPrtGkkSpzMLv7iiukfQWl2krvrts7tIFnMs3sc9JO34ZMo0EwdI1Fz1sv1bNH0HmZK/nuMqHjxX+1YQx5gCnooYec9G8Uo5gdmdNCjcxKUEDGJ95bUKvMSB8Lm9dIksRTBQmR+Tb42lntA1A5T0TcBfNfX6NH6zbJlhKIJ7GDAsnvMVAmbxNcZY6rmRWqW+Dw== 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 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. Thanks, Kemeng > > What might have confused you is that GDTC_INIT_NO_WB is defined to be empty > when CONFIG_CGROUP_WRITEBACK is disabled. But this is only because in that > case dtc_dom() function unconditionally returns global_wb_domain so we > don't bother with initializing (or even having) the 'dom' field anywhere. > > Now I agree this whole code is substantially confusing and complex and it > would all deserve some serious thought how to make it more readable. But > even after thinking about it again I don't think removing GDTC_INIT_NO_WB is > the right way to go. > > Honza >