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Mon, 07 Dec 2020 18:29:59 -0800 (PST) MIME-Version: 1.0 References: <20201206101451.14706-1-songmuchun@bytedance.com> <20201207130018.GJ25569@dhcp22.suse.cz> <20201207150254.GL25569@dhcp22.suse.cz> <30ebae81-86e8-80db-feb6-d7c47dbaccb2@infradead.org> In-Reply-To: <30ebae81-86e8-80db-feb6-d7c47dbaccb2@infradead.org> From: Muchun Song Date: Tue, 8 Dec 2020 10:29:23 +0800 Message-ID: Subject: Re: [External] Re: [RESEND PATCH v2 00/12] Convert all vmstat counters to pages or bytes To: Randy Dunlap Cc: Michal Hocko , Greg KH , rafael@kernel.org, Alexey Dobriyan , Andrew Morton , Johannes Weiner , Vladimir Davydov , Hugh Dickins , Will Deacon , Roman Gushchin , Mike Rapoport , Thomas Gleixner , esyr@redhat.com, peterx@redhat.com, krisman@collabora.com, Suren Baghdasaryan , avagin@openvz.org, Marco Elver , Joonsoo Kim , LKML , linux-fsdevel , Linux Memory Management List , Cgroups Content-Type: text/plain; charset="UTF-8" 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: On Tue, Dec 8, 2020 at 2:51 AM Randy Dunlap wrote: > > On 12/7/20 7:02 AM, Michal Hocko wrote: > > On Mon 07-12-20 22:52:30, Muchun Song wrote: > >> On Mon, Dec 7, 2020 at 9:00 PM Michal Hocko wrote: > >>> > >>> On Sun 06-12-20 18:14:39, Muchun Song wrote: > >>>> Hi, > >>>> > >>>> This patch series is aimed to convert all THP vmstat counters to pages > >>>> and some KiB vmstat counters to bytes. > >>>> > >>>> The unit of some vmstat counters are pages, some are bytes, some are > >>>> HPAGE_PMD_NR, and some are KiB. When we want to expose these vmstat > >>>> counters to the userspace, we have to know the unit of the vmstat counters > >>>> is which one. It makes the code complex. Because there are too many choices, > >>>> the probability of making a mistake will be greater. > >>>> > >>>> For example, the below is some bug fix: > >>>> - 7de2e9f195b9 ("mm: memcontrol: correct the NR_ANON_THPS counter of hierarchical memcg") > >>>> - not committed(it is the first commit in this series) ("mm: memcontrol: fix NR_ANON_THPS account") > >>>> > >>>> This patch series can make the code simple (161 insertions(+), 187 deletions(-)). > >>>> And make the unit of the vmstat counters are either pages or bytes. Fewer choices > >>>> means lower probability of making mistakes :). > >>>> > >>>> This was inspired by Johannes and Roman. Thanks to them. > >>> > >>> It would be really great if you could summarize the current and after > >>> the patch state so that exceptions are clear and easier to review. The > >> > >> Agree. Will do in the next version. Thanks. > >> > >> > >>> existing situation is rather convoluted but we have at least units part > >>> of the name so it is not too hard to notice that. Reducing exeptions > >>> sounds nice but I am not really sure it is such an improvement it is > >>> worth a lot of code churn. Especially when it comes to KB vs B. Counting > >> > >> There are two vmstat counters (NR_KERNEL_STACK_KB and > >> NR_KERNEL_SCS_KB) whose units are KB. If we do this, all > >> vmstat counter units are either pages or bytes in the end. When > >> we expose those counters to userspace, it can be easy. You can > >> reference to: > >> > >> [RESEND PATCH v2 11/12] mm: memcontrol: make the slab calculation consistent > >> > >> From this point of view, I think that it is worth doing this. Right? > > > > Well, unless I am missing something, we have two counters in bytes, two > > in kB, both clearly distinguishable by the B/KB suffix. Changing KB to B > > will certainly reduce the different classes of units, no question about > > that, but I am not really sure this is worth all the code churn. Maybe > > others will think otherwise. > > > > As I've said the THP accounting change makes more sense to me because it > > allows future changes which are already undergoing so there is more > > merit in those. > > > > Hi, > > Are there any documentation changes that go with these patches? > Or are none needed? > > If the patches change the output in /proc/* or /sys/* then I expect > there would need to be some doc changes. Oh, we do not change the output. It is transparent to userspace. Thanks. > > And is there any chance of confusing userspace s/w (binary or scripts) > with these changes? > > thanks. > -- > ~Randy > -- Yours, Muchun