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Shutemov" Cc: Matthew Wilcox , akpm@linux-foundation.org, hughd@google.com, david@redhat.com, wangkefeng.wang@huawei.com, 21cnbao@gmail.com, ryan.roberts@arm.com, ioworker0@gmail.com, da.gomez@samsung.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Kirill A . Shutemov" References: <6dohx7zna7x6hxzo4cwnwarep3a7rohx4qxubds3uujfb7gp3c@2xaubczl2n6d> <8e48cf24-83e1-486e-b89c-41edb7eeff3e@linux.alibaba.com> From: Baolin Wang In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Stat-Signature: urztifi4qo68mgyexh5aqrzkzhee9tth X-Rspamd-Queue-Id: 6C0701C0005 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1729568053-688711 X-HE-Meta: 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 ufLSvin1 Cgx3/HIeDkwIIfDtLA3YTPDbxk1a9uyJFbDW1fCQlZl/QgqOmAEJdrsihm1KsnV8Ocu6db5y51LcYPzpAih3Ix4sytyQUgKQC0lNUOnYf7msx7ErHkX+Zl3zGOnAgqYYw64D9bJ5//y9CApckxxNLeLHiaPOjWPM5xkSlEJuwpoRU5+AH1a+hZc8kd6C465pBDhfRsnLZpEANpWY2d7NANXZfKXGci0a6zYy3Fc6KWI+kaknt+v/W9WSgtkz6SIgPVOXIpxxYCSY6jMWuCzO3Fs2vVQ== 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 2024/10/21 16:54, Kirill A. Shutemov wrote: > On Mon, Oct 21, 2024 at 02:24:18PM +0800, Baolin Wang wrote: >> >> >> On 2024/10/17 19:26, Kirill A. Shutemov wrote: >>> On Thu, Oct 17, 2024 at 05:34:15PM +0800, Baolin Wang wrote: >>>> + Kirill >>>> >>>> On 2024/10/16 22:06, Matthew Wilcox wrote: >>>>> On Thu, Oct 10, 2024 at 05:58:10PM +0800, Baolin Wang wrote: >>>>>> Considering that tmpfs already has the 'huge=' option to control the THP >>>>>> allocation, it is necessary to maintain compatibility with the 'huge=' >>>>>> option, as well as considering the 'deny' and 'force' option controlled >>>>>> by '/sys/kernel/mm/transparent_hugepage/shmem_enabled'. >>>>> >>>>> No, it's not. No other filesystem honours these settings. tmpfs would >>>>> not have had these settings if it were written today. It should simply >>>>> ignore them, the way that NFS ignores the "intr" mount option now that >>>>> we have a better solution to the original problem. >>>>> >>>>> To reiterate my position: >>>>> >>>>> - When using tmpfs as a filesystem, it should behave like other >>>>> filesystems. >>>>> - When using tmpfs to implement MAP_ANONYMOUS | MAP_SHARED, it should >>>>> behave like anonymous memory. >>>> >>>> I do agree with your point to some extent, but the ‘huge=’ option has >>>> existed for nearly 8 years, and the huge orders based on write size may not >>>> achieve the performance of PMD-sized THP in some scenarios, such as when the >>>> write length is consistently 4K. So, I am still concerned that ignoring the >>>> 'huge' option could lead to compatibility issues. >>> >>> Yeah, I don't think we are there yet to ignore the mount option. >> >> OK. >> >>> Maybe we need to get a new generic interface to request the semantics >>> tmpfs has with huge= on per-inode level on any fs. Like a set of FADV_* >>> handles to make kernel allocate PMD-size folio on any allocation or on >>> allocations within i_size. I think this behaviour is useful beyond tmpfs. >>> >>> Then huge= implementation for tmpfs can be re-defined to set these >>> per-inode FADV_ flags by default. This way we can keep tmpfs compatible >>> with current deployments and less special comparing to rest of >>> filesystems on kernel side. >> >> I did a quick search, and I didn't find any other fs that require PMD-sized >> huge pages, so I am not sure if FADV_* is useful for filesystems other than >> tmpfs. Please correct me if I missed something. > > What do you mean by "require"? THPs are always opportunistic. > > IIUC, we don't have a way to hint kernel to use huge pages for a file on > read from backing storage. Readahead is not always the right way. IIUC, most file systems use method similar to iomap buffered IO (see iomap_get_folio()) to allocate huge pages. What I mean is that, it would be better to have a real use case to add a hint for allocating THP (other than tmpfs). >>> If huge= is not set, tmpfs would behave the same way as the rest of >>> filesystems. >> >> So if 'huge=' is not set, tmpfs write()/fallocate() can still allocate large >> folios based on the write size? If yes, that means it will change the >> default huge behavior for tmpfs. Because previously having 'huge=' is not >> set means the huge option is 'SHMEM_HUGE_NEVER', which is similar to what I >> mentioned: >> "Another possible choice is to make the huge pages allocation based on write >> size as the *default* behavior for tmpfs, ..." > > I am more worried about breaking existing users of huge pages. So changing > behaviour of users who don't specify huge is okay to me. OK. Good.