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lance.yang@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] mm: shmem: don't set large-order range for internal shmem mount Date: Wed, 15 Apr 2026 21:52:38 -0400 X-Mailer: MailMate (2.0r6290) Message-ID: In-Reply-To: <907b3a20-52b3-4969-8456-bd3a8d2571f2@linux.alibaba.com> References: <2d138a3f-0006-4a01-852a-4570d7ba781d@linux.alibaba.com> <1a3cb6b2-94e0-4268-8cd9-1f9a9deb6c6b@linux.alibaba.com> <875dc63b-0cd2-49e5-8b0d-3fb062789813@kernel.org> <846B17B0-1BAF-4959-8FC2-42744C44B1D6@nvidia.com> <16745f2b-b008-4df1-ac76-f18b4a826dbd@linux.alibaba.com> <4AD72E13-C4AE-4ADA-8AB2-DDB3CEE6A527@nvidia.com> <907b3a20-52b3-4969-8456-bd3a8d2571f2@linux.alibaba.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: MN2PR01CA0043.prod.exchangelabs.com (2603:10b6:208:23f::12) To DS7PR12MB9473.namprd12.prod.outlook.com (2603:10b6:8:252::5) MIME-Version: 1.0 X-MS-PublicTrafficType: Email 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tFSOcsMWKL3TcL3bsom+lWorA4n0tiAiEGgiBeGsVduwF/EOXwL1RRB50tZgrtNVpdpBfFuJIqp2m+jwsGCuirKqM3Gk3M3YVluJZoOEl2y66kUa4X9YK2+Px6Kv7+5BFTbrGVPg1Y5Lqv/Auf9Hb0UpBDZamAupgFthEfcWuzkmAJe/LV40DKe+fUwoh39GcJAta1fciw3Zqc+SJDHWN5M8R4GNOpInzCpRimXKzNhJR70qLWYWVKpTByEXE6dZNHMUFXCnsqfM34Clc5UdRyeBJn1Ld765+HFhi5ikHF4JXHIcCEEv8sZjwBBOOZf+Y8EP6rqIAV9VSm6WLGgSD7nys4sGXqE5U9/5m9AQxNhN4dlV/8XmgYLpNbiQAMd6KIjzTNFpW1SWfoyrDqyPAJI+kpdzQb1OIEpC+PngkVYNbLYQ= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 15 Apr 2026, at 21:45, Baolin Wang wrote: > On 4/16/26 9:36 AM, Zi Yan wrote: >> On 15 Apr 2026, at 21:22, Baolin Wang wrote: >> >>> On 4/16/26 9:11 AM, Zi Yan wrote: >>>> On 15 Apr 2026, at 21:05, Baolin Wang wrote: >>>> >>>>> On 4/15/26 10:36 PM, David Hildenbrand (Arm) wrote: >>>>>> On 4/15/26 12:05, Baolin Wang wrote: >>>>>>> >>>>>>> >>>>>>> On 4/15/26 5:54 PM, David Hildenbrand (Arm) wrote: >>>>>>>>> >>>>>>>>> Yes, that makes sense. >>>>>>>>> >>>>>>>>> However, it=E2=80=99s also possible that the mapping does not sup= port large >>>>>>>>> folios, yet anonymous shmem can still allocate large folios via t= he >>>>>>>>> sysfs interfaces. That doesn't make sense, right? >>>>>>>> >>>>>>>> That's what I am saying: if there could be large folios in there, = then >>>>>>>> let's tell the world. >>>>>>>> >>>>>>>> Getting in a scenario where the mapping claims to not support larg= e >>>>>>>> folios, but then we have large folios in there is inconsistent, no= t? >>>>>>>> >>>>>>>> [...] >>>>>>>> >>>>>>>>> >>>>>>>>> For the current anonymous shmem (tmpfs is already clear, no quest= ions), >>>>>>>>> I don=E2=80=99t think there will be any "will never have/does nev= er allow" >>>>>>>>> cases, because it can be changed dynamically via the sysfs interf= aces. >>>>>>>> >>>>>>>> Right. It's about non-anon shmem with huge=3Doff. >>>>>>>> >>>>>>>>> >>>>>>>>> If we still want that logic, then for anonymous shmem we can trea= t it as >>>>>>>>> always "might have large folios". >>>>>>> >>>>>>> OK. To resolve the confusion about 1, the logic should be changed a= s >>>>>>> follows. Does that make sense to you? >>>>>>> >>>>>>> if (sbinfo->huge || (sb->s_flags & SB_KERNMOUNT)) >>>>>>> =C2=A0=C2=A0=C2=A0=C2=A0mapping_set_large_folios(inode->i_mappin= g); >>>>>> >>>>>> I think that's better. >>>>> >>>>> Thanks for your valuable input. >>>>> >>>>> But has Willy says, maybe we can just >>>>>> unconditionally set it and have it even simpler. >>>>> >>>>> However, for tmpfs mounts, we should still respect the 'huge=3D' moun= t option. See commit 5a90c155defa ("tmpfs: don't enable large folios if not= supported"). >>>> >>>> Is it possible to get sbinfo->huge during tmpfs=E2=80=99s folio alloca= tion time, so that >>>> even if all tmpfs has mapping_set_large_folios() but sbinfo->huge can = still >>>> decide whether huge page will be allocated for a tmpfs? >>> >>> Yes, of course. However, the issue isn=E2=80=99t whether tmpfs allows a= llocating large folios. >>> >>> The problem commit 5a90c155defa tries to fix is that when tmpfs is moun= ted with the 'huge=3Dnever' option, we will not allocate large folios for i= t. Then when writing tmpfs files, generic_perform_write() will call mapping= _max_folio_size() to get the chunk size and ends up with an order-9 size fo= r writing tmpfs files. However, this tmpfs file is populated only with smal= l folios, resulting in a performance regression. >> >> IIUC, generic_perform_write() needs to use a small chunk if tmpfs denies= huge. >> It seems that Kefeng did that in the first try[1]. But willy suggested >> the current fix. >> >> I wonder if we should revisit Kefeng=E2=80=99s first version. >> >> [1] https://lore.kernel.org/all/20240914140613.2334139-1-wangkefeng.wang= @huawei.com/ > > Personally, I still prefer the current fix (commit 5a90c155defa). We shou= ld honor the tmpfs mount option. If it explicitly says no large folios, we = shouldn=E2=80=99t call mapping_set_large_folios(). Isn=E2=80=99t that more = consistent with its semantics? Filesystems wishing to turn on large folios in the pagecache should call ``mapping_set_large_folios`` when initializing the incore inode. You mean tmpfs with huge option set is a FS wishing to turn on large folios in the pagecache, otherwise it is a FS wishing not to have large fol= io in the pagecache. tmpfs with different options is seen as different FSes. Best Regards, Yan, Zi