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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: EFE0940015 X-Stat-Signature: 391yfhgn84okthnsce7se6hij4t5xuza X-Rspam-User: X-HE-Tag: 1720511670-819554 X-HE-Meta: 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 hYbkv6LL GhnEb5Srk/IcFMZE0+843vaktOm5tbckWrDV/923Y/NsDWzprDgGg+37oJwxJybYrKf0O1eYZUTwULQtaZgDKNYoDAjYgeI+w69wFvzvEptJQJGLn4bPE1URWU/13PSx/yAiYQw62poW2V0C3giZWyNT25aW3oAQbyU/LlQyiur3mNSbhNoFHR+Kvdoo6r0TJIxyM5Phf0ILL/RJzafCSq5v/s63S61sc3Ur+FDl22ZY2FLwTnxtMzZp0YYvAuFrBmw0km9SR1x1AARg+9mfhsKhYGbmLd/bJMXlWYWAjv9tsiO96CFw7Uh3DnviwOupRLnJVyv/ft2Zef+SdZVryBb7gJd7kP6aWy+SUUQ/L2Oq3iuxsv3rTKYVlCRMBZNdaytnMDKqKwm+0l9H/v2k9Cxbzai/PAgeBHqPXCgDuaGwbOhJ6DDBXpFavmvUcopuOlS4qBpYJTsfX1++DXQgZ/HLt16iS/dN2XdET 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 09.07.24 09:47, Ryan Roberts wrote: > On 08/07/2024 21:50, David Hildenbrand wrote: >> On 08.07.24 14:29, Ryan Roberts wrote: >>> On 08/07/2024 12:36, Barry Song wrote: >>>> On Mon, Jul 8, 2024 at 11:24 PM Ryan Roberts wrote: >>>>> >>>>> The legacy PMD-sized THP counters at /proc/vmstat include >>>>> thp_file_alloc, thp_file_fallback and thp_file_fallback_charge, which >>>>> rather confusingly refer to shmem THP and do not include any other types >>>>> of file pages. This is inconsistent since in most other places in the >>>>> kernel, THP counters are explicitly separated for anon, shmem and file >>>>> flavours. However, we are stuck with it since it constitutes a user ABI. >>>>> >>>>> Recently, commit 66f44583f9b6 ("mm: shmem: add mTHP counters for >>>>> anonymous shmem") added equivalent mTHP stats for shmem, keeping the >>>>> same "file_" prefix in the names. But in future, we may want to add >>>>> extra stats to cover actual file pages, at which point, it would all >>>>> become very confusing. >>>>> >>>>> So let's take the opportunity to rename these new counters "shmem_" >>>>> before the change makes it upstream and the ABI becomes immutable. >>>> >>>> Personally, I think this approach is much clearer. However, I recall >>>> we discussed this >>>> before [1], and it seems that inconsistency is a concern? >>> >>> Embarrassingly, I don't recall that converstation at all :-| but at least what I >>> said then is consistent with what I've done in this patch. >>> >>> I think David's conclusion from that thread was to call them FILE_, and add both >>> shmem and pagecache counts to those counters, meaning we can keep the same name >>> as legacy THP counters. But those legacy THP counters only count shmem, and I >>> don't think we would get away with adding pagecache counts to those at this >>> point? (argument: they have been around for long time and there is a risk that >>> user space relies on them and if they were to dramatically increase due to >>> pagecache addition now that could break things). In that case, there is still >>> inconsistency, but its worse; the names are consistent but the semantics are >>> inconsistent. >>> >>> So my vote is to change to SHMEM_ as per this patch :) >> >> I also forgot most of the discussion, but these 3 legacy counters are really >> only (currently) incremented for shmem. I think my idea was to keep everything >> as FILE_ for now, maybe at some point make the pagecache also use them, and then >> maybe have separate FILE_ + SHMEM_. >> >> But yeah, likely it's best to only have "shmem" here for now, because who knows >> what we can actually change about the legacy counters. But it's always though >> messing with legacy stuff that is clearly suboptimal ... > > Sorry David, I've read your response a bunch of times and am still not > completely sure what you are advocating for. > > To make my proposal crystal clear, I think we should leave the legacy counters > alone - neither change their name nor what they count (which is _only_ shmem). I > think we should rename the new mTHP counters to "shmem" and have them continue > to only count shmem. Then additionally, I think we should introduce new "file" > mTHP counters that count the page cache allocations (that's a future set of > patches, which I'm working on together with user controls to determine which > mTHP sizes can be used by page cache). > > As suggested by Barry, I propose to also improve the documentation for the > legacy counters to make it clear that dispite their name being "file" they are > actually counting "shmem". I'll do this for v2. Yes, and please. Likely we should document for the legacy ones (if not already done) that they only track PMD-sized THPs. > > David, would you support this approach? If so, I'd like to push this forwards > asap so that it gets into v6.11 to avoid ever exposing the mthp counters with > the "file" name. Yes, sorry for not being clear. -- Cheers, David / dhildenb