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Mon, 08 Jul 2024 18:21:20 -0700 (PDT) MIME-Version: 1.0 References: <20240708112445.2690631-1-ryan.roberts@arm.com> <744749c3-4506-40d9-ac48-0dbc59689f92@arm.com> <10b201b1-53d3-4f62-be8e-996aa95d2b99@redhat.com> In-Reply-To: <10b201b1-53d3-4f62-be8e-996aa95d2b99@redhat.com> From: Lance Yang Date: Tue, 9 Jul 2024 09:21:09 +0800 Message-ID: Subject: Re: [PATCH v1] mm: shmem: Rename mTHP shmem counters To: David Hildenbrand Cc: Ryan Roberts , Barry Song , Andrew Morton , Hugh Dickins , Jonathan Corbet , Baolin Wang , Matthew Wilcox , Zi Yan , Daniel Gomez , linux-kernel@vger.kernel.org, linux-mm@kvack.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: D8243140006 X-Stat-Signature: 3iikmxbdi5ucse3urppifgjbedmd6grt X-Rspam-User: X-HE-Tag: 1720488082-162884 X-HE-Meta: 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 PC9WmaN9 G4OycVSuEBAOZjmEX1A5dVs7uyVPIMAW9mqfKZVPhcrTQRQIJ5nwRVLhjpWIyTC+gQ3bXXWsMJgKbeyeVN2H3QrJU/FHmGO3OixJPonI9tWPwLOH4Lk648wVuO8brn9cdozcypFljmf92RE92f6eGztbQqwN0CNiPbcXeA1CoE2pRDblNxJkoMyzEGsFRIq5hamjlZ8x2euqxRQvxd107VlwBniuGsZWE/hdGOcFPYXq7vnkUIelqZPMzDcDsuTHhSNngBFLmXB2UkSS8bnF/UzX3XS/KtvWPkWTr1Nfj1geiCxjLKO/txUsF7ADwAAwZCRkpmSz4kF5mhVr3ipx8KVwQ/ibEzgCTMgjk35ogsxSTaDw4VlzGpOjEER07n9cZYX5+ 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 Tue, Jul 9, 2024 at 4:50=E2=80=AFAM 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=E2=80=AFPM 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 ty= pes > >>> of file pages. This is inconsistent since in most other places in the > >>> kernel, THP counters are explicitly separated for anon, shmem and fil= e > >>> flavours. However, we are stuck with it since it constitutes a user A= BI. > >>> > >>> 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 lea= st 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 s= ame 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 ri= sk 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 semantic= s 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 .= .. Couldn't agree more! It's never an easy task to handle such matters :) Perhaps, the time has come for us to separate FILE_ and SHMEM_. Thanks, Lance > > -- > Cheers, > > David / dhildenb >