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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: kbdbypdi8j9dmwi4yyqp9fwfchcaj5xt X-Rspamd-Queue-Id: C14664000D X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1730108901-181033 X-HE-Meta: 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 B1xHx/KX p+w85qiFgu2ETrQZtcW6+Z/FlbdwJX5swhDoXo5tHg4DTnwTeV0+I0h60XXNG1YqPT1oQjGsgZ/FyERCxbj0RkX/MbNrvCXfJ/O1PvUESbpaMY+I/D8HFvVitijMRqk6kH8VlMAgvBg63zoXwTglLkvqeeDK2vFDDfaFdvzXyFH7YuoyxK4gIBZT/5OoBLz8tBusaBPdabd0FA5m7IBLV7a0r4axB5cCy0wvcZd6O3LpoIPGGpXAG3jGYVGVcByDX03m4gfOaV/oryEPbtHxhYq8EUpb8Xl01hTNJ9aVsr59eq8SmjTPQMBFXxr3iV35ZbNCRN6YlwaDGjUHsZ2V7yib5TCbeDgCDiEUwJygHBWLZGc3nuy6CmmhaepEme2bwC5bxtRZv1BEnvUI9fMyVfV08zQphhgWfILC35D6W0sNRA1F9m79rpQCsPRsj+vME6SZSzJmwEGOghWk= 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 25.10.24 22:21, David Hildenbrand wrote: > Sorry for the late reply! > >>>>>> IMHO, as I discussed with Kirill, we still need maintain compatibility >>>>>> with the 'huge=' mount option. This means that if 'huge=never' is set >>>>>> for tmpfs, huge page allocation will still be prohibited (which can >>>>>> address Hugh's request?). However, if 'huge=' is not set, we can >>>>>> allocate large folios based on the write size. >> >> So, in order to make tmpfs behave like other filesystems, we need to >> allocate large folios by default. Not setting 'huge=' is the same as >> setting it to 'huge=never' as per documentation. But 'huge=' is meant to >> control THP, not large folios, so it should not have a conflict here, or >> else, what case are you thinking? > > I think we really have to move away from "huge/thp == PMD", that's a > historical artifact. Everything else will simply be inconsistent and > confusing in the future -- and I don't see any real need for that. For > anonymous memory and anon shmem we managed the transition. (there is a > longer writeup from me about this topic, so I won't go into detail). > > > I think I raised this in the past, but tmpfs/shmem is just like any > other file system .. except it sometimes really isn't and behaves much > more like (swappable) anonymous memory. (or mlocked files) > > There are many systems out there that run without swap enabled, or with > extremely minimal swap (IIRC until recently kubernetes was completely > incompatible with swapping). Swap can even be disabled today for shmem > using a mount option. > > That's a big difference to all other file systems where you are > guaranteed to have backend storage where you can simply evict under > memory pressure (might temporarily fail, of course). > > I *think* that's the reason why we have the "huge=" parameter that also > controls the THP allocations during page faults (IOW possible memory > over-allocation). Maybe also because it was a new feature, and we only > had a single THP size. > > There is, of course also the "fallocate() might not free up memory if > there is an unexpected reference on the page because splitting it will > fail" problem, that even exists when not over-allocating memory in the > first place ... > > > So ...I don't think tmpfs behaves like other file system in some cases. > And I don't think ignoring these points is a good idea. > > Fortunately I don't maintain that code :) > > > If we don't want to go with the shmem_enabled toggles, we should > probably still extend the documentation to cover "all THP sizes", like > we did elsewhere. > > huge=never: no THPs of any size > huge=always: THPs of any size (fault/write/etc) > huge=fadvise: like "always" but only with fadvise/madvise > huge=within_size: like "fadvise" but respect i_size Thinking some more about that over the weekend, this is likely the way to go, paired with conditionally changing the default to always/within_size. I suggest a kconfig option for that. That should probably do as a first shot; I assume people will want more control over which size to use, especially during page faults, but that can likely be added later. -- Cheers, David / dhildenb