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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776419560; bh=S1dWoomNg7jU2+LlZH898XUljhPwIL130Eucg4xZC/E=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=RcSHu6Wqh7GfxjLFP0/VIaIK8sPxC/5pSCoKoTaO1OtdwBEtK1Rq8iC6lJY7+G7UF yMu4MaTe9Ss4SDyRA3OHEB+KaZqikGhh5oxqUOiBH1jQrLQMSxbSJ6vzSQwnJgxpT5 I+wbHAXPf7kGvnpQP1ILZmxclCFkuuSkv5YwYRnNGlyDeiWKYeHTIxstt7q5iSkmqC OZcIw8o1oBZX3pQkmZTqi7o3AR4r9OIiNSi+93CC7iajjuuLH59XJxSsgQK7nlEsWI BZL3BYJeFjlr+G4LXHYg9G0MG3Le9UXWQ+nVkoHvJbhyLZS9MqhA5Na73kIHh+SE2K IwdyUEsgi0PDQ== Message-ID: Date: Fri, 17 Apr 2026 11:52:36 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mm: shmem: always support large folios for internal shmem mount To: Baolin Wang , akpm@linux-foundation.org, hughd@google.com Cc: willy@infradead.org, ziy@nvidia.com, ljs@kernel.org, lance.yang@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <26f954be62348591e720c4e8b7a9099b74dc1d6d.1776331555.git.baolin.wang@linux.alibaba.com> <1b3c0401-6d10-4a28-97c8-8e3858d8dc3d@kernel.org> <015de194-99b9-4f9e-8c89-d35807c6fd08@linux.alibaba.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 8D3AD180002 X-Rspamd-Server: rspam12 X-Stat-Signature: 6shb8dwxmtxhh7xy7q8ejmothq3q6tra X-Rspam-User: X-HE-Tag: 1776419561-946103 X-HE-Meta: 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 oMOXuGnu no+gqK3u84eZBVlunnKZPl9mC+cGdlaDJTBZiurgO5aoBslTyU+CX5zfnXca82j1y/XIvEIDUiATkiLUEPYM1CmIfv1Vjr06YliI0HDAtflQjbIuMA+E3ROFudao+xQRAGa1KAB5hoTAsv1Hc2KS4phMi3rA6fwsv07XQsOzzoAJH9xO4oMrcKMLkJCUjQKO1YJHTtajOPNEUWBsWrVhHawvnwIqauNQPp09y6o8AvP6kp/aINGFS4Up8w23MD0smavBP1S5fXV168I/t4pLPZ4PBJ2wbw3KjLuuki/5vbru3n89Gg4UNcGqsmY0lwVb71p64plqdDg9wfek= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 4/17/26 11:27, Baolin Wang wrote: > > > On 4/17/26 5:21 PM, David Hildenbrand (Arm) wrote: >> On 4/17/26 05:25, Baolin Wang wrote: >>> Currently, when shmem mounts are initialized, they only use 'sbinfo- >>> >huge' to >>> determine whether the shmem mount supports large folios. However, for >>> anonymous >>> shmem, whether it supports large folios can be dynamically configured >>> via sysfs >>> interfaces, so setting or not setting mapping_set_large_folios() >>> during initialization >>> cannot accurately reflect whether anonymous shmem actually supports >>> large folios, >>> which has already caused some confusion[1]. >>> >>> As discussed with David[2], for anonymous shmem we can treat it as >>> always potentially >>> having large folios. Therefore, always support large folios for the >>> internal shmem >>> mount (e.g., anonymous shmem), and which large order allocations are >>> allowed can be >>> configured dynamically via the 'shmem_enabled' interfaces. >>> >>> [1] https://lore.kernel.org/all/ >>> ec927492-4577-4192-8fad-85eb1bb43121@linux.alibaba.com/ >>> [2] https://lore.kernel.org/ >>> all/875dc63b-0cd2-49e5-8b0d-3fb062789813@kernel.org/ >>> Signed-off-by: Baolin Wang >>> --- >>> Changes from v2: >>>   - Always support large folios for internal shmem mount, per David. >>> Changes from v1: >>>   - Update the comments and commit message, per Lance. >>> --- >>>   mm/shmem.c | 13 +++++++++++-- >>>   1 file changed, 11 insertions(+), 2 deletions(-) >>> >>> diff --git a/mm/shmem.c b/mm/shmem.c >>> index 4ecefe02881d..769ef37b1ea9 100644 >>> --- a/mm/shmem.c >>> +++ b/mm/shmem.c >>> @@ -3088,8 +3088,17 @@ static struct inode *__shmem_get_inode(struct >>> mnt_idmap *idmap, >>>       if (sbinfo->noswap) >>>           mapping_set_unevictable(inode->i_mapping); >>>   -    /* Don't consider 'deny' for emergencies and 'force' for >>> testing */ >>> -    if (sbinfo->huge) >>> +    /* >>> +     * Always support large folios for the internal shmem mount (e.g., >>> +     * anonymous shmem), and which large order allocations are allowed >>> +     * can be configured dynamically via the 'shmem_enabled' >>> interfaces. >>> +     * >>> +     * For tmpfs, honour the 'huge=' mount option to determine whether >>> +     * large folios are supported. >>> +     * >>> +     * Note: don't consider 'deny' for emergencies and 'force' for >>> testing. >>> +     */ >>> +    if (sbinfo->huge || (sb->s_flags & SB_KERNMOUNT)) >>>           mapping_set_large_folios(inode->i_mapping); >> >> Two questions from a non-fs person about the semantics here: >> >> a) Can sbinfo->huge be triggered later, for example, through a remount >> (staring at shmem_reconfigure()) > > For tmpfs, yes. So, we could pass this check here, not setting mapping_set_large_folios(), but later someone toggles it and we missed to set mapping_set_large_folios()? Or would we always go through another __shmem_get_inode() after a remount? -- Cheers, David