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Sat, 03 Oct 2026 08:09:44 -0700 (PDT) X-Received: by 2002:a05:620a:4113:b0:93a:f9:614a with SMTP id af79cd13be357-93cf1748ff3mr1013742585a.34.1791040184161; Sat, 03 Oct 2026 08:09:44 -0700 (PDT) Received: from [192.168.2.110] ([142.172.30.162]) by smtp.gmail.com with ESMTPSA id af79cd13be357-93e457a4e20sm361949485a.40.2026.10.03.08.09.42 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 03 Oct 2026 08:09:43 -0700 (PDT) Message-ID: <0162d0f5-8e75-458b-a0a1-6071f46d4b35@redhat.com> Date: Sat, 3 Oct 2026 11:09:42 -0400 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v8 07/14] mm: shmem: allow THP support determination at folio allocation time To: "David Hildenbrand (Arm)" , linux-kernel@vger.kernel.org, linux-mm@kvack.org, baolin.wang@linux.alibaba.com, ziy@nvidia.com, lance.yang@linux.dev Cc: corbet@lwn.net, tsbogend@alpha.franken.de, maddy@linux.ibm.com, mpe@ellerman.id.au, agordeev@linux.ibm.com, gerald.schaefer@linux.ibm.com, hca@linux.ibm.com, gor@linux.ibm.com, x86@kernel.org, tglx@kernel.org, mingo@redhat.com, bp@alien8.de, hughd@google.com, dave.hansen@linux.intel.com, djbw@kernel.org, vishal.l.verma@intel.com, dave.jiang@intel.com, akpm@linux-foundation.org, yintirui@huawei.com, dev.jain@arm.com, usama.arif@linux.dev References: From: Luiz Capitulino In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: B9WLHAhdcaBE14MS5IzX7LORo1LN7RcSd4S7IICrxGg_1791040185 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 18B7140002 X-Rspam-User: X-Rspamd-Server: rspam07 X-Stat-Signature: 7s3h9u4hyy1fpos85794a6obopmfkpyf X-HE-Tag: 1791040186-260800 X-HE-Meta: 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 As3953Xd U2bmP/vZH9aZPgbjign1YE2XYhieDh91NpEW3Z4LstBnMtvFLAqDeNKPL6e179BH1yP5UMO4u0gDeTRUy7t1isONlYzDkMMQbvLz/lQ1wji/xEKhDBbgyJb7V/bO6jp9gBwaDPLvNysgMchnDN53tQSNq3q/5IUG2Xjkr9jVVuPPsRqtcevxpMyhFr5nD03VJarw5E6h12EdzC+Agt+0zH85S5H3BaUqoO+r7VqhKJGswc9oZIfTqhFZAyMSKHuhepZJAMr3d+4ATlXvgteKHMAYgCb+uqEG4C7P5mbcefR/yQpo1Sa/kwPmMcv9KyP0PyXIcS9mmn1OrNsEV/vfJMrrMAMKo8vVobW1lLuFbKKwFupAdI4bvzJUHzPaqGqvBhfiS Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 10/2/26 3:23 PM, David Hildenbrand (Arm) wrote: > On 9/18/26 03:45, Luiz Capitulino wrote: >> In order to enable THP support in shmem today, besides the user >> configuration required, the CPU must support PMD-sized pages. This >> is the case because of the following has_transparent_hugepage() >> usage: >> >> - shmem_parse_one() and shmem_parse_huge(): Check if THP is built-in and >> if the CPU supports PMD-sized pages >> >> - shmem_init(): Since the CONFIG_TRANSPARENT_HUGEPAGE guard is outside >> the code block calling has_transparent_hugepage(), the >> has_transparent_hugepage() call is exclusively checking if the CPU >> supports PMD-sized pages >> >> While it's necessary to check if CONFIG_TRANSPARENT_HUGEPAGE is enabled >> in all cases, shmem can determine THP size support at folio allocation >> time. Therefore, drop the has_transparent_hugepage() usage listed above >> while keeping the CONFIG_TRANSPARENT_HUGEPAGE checks. >> >> Additionally, we need to check if PMD size order is supported in >> shmem_getattr(). Use pgtable_has_pmd_leaves() for that. >> >> Reviewed-by: Baolin Wang >> Signed-off-by: Luiz Capitulino >> --- >> mm/shmem.c | 9 +++++---- >> 1 file changed, 5 insertions(+), 4 deletions(-) >> >> diff --git a/mm/shmem.c b/mm/shmem.c >> index 776dff8a848e..930657d05375 100644 >> --- a/mm/shmem.c >> +++ b/mm/shmem.c >> @@ -690,7 +690,7 @@ static int shmem_parse_huge(const char *str) >> else >> return -EINVAL; >> >> - if (!has_transparent_hugepage() && >> + if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && >> huge != SHMEM_HUGE_NEVER && huge != SHMEM_HUGE_DENY) >> return -EINVAL; >> >> @@ -1524,6 +1524,8 @@ static int shmem_getattr(struct mnt_idmap *idmap, >> generic_fillattr(idmap, request_mask, inode, stat); >> >> orders = shmem_huge_global_enabled(inode, 0, 0, false, NULL, 0); > > I'm curious: why is that not handled inside shmem_huge_global_enabled() ? If PMD > order is impossible (well, okay, it is possible, but we simply cannot map these > things through PMDs), I would expect that we never list them as "enabled". Yes, you're right. What about renaming current shmem_huge_global_enabled() to __shmem_huge_global_enabled() and then having: static unsigned int shmem_huge_global_enabled(struct inode *inode, pgoff_t index, loff_t write_end, bool shmem_huge_force, struct vm_area_struct *vma, vm_flags_t vm_flags) { unsigned int orders; orders = __shmem_huge_global_enabled(inode, index, write_end, shmem_huge_force, vma, vm_flags); if (!pgtable_has_pmd_leaves()) orders &= ~BIT(PMD_ORDER); return orders; } Would this be acceptable? > > (while shmem could allocate PMD folios, it would have to map them always through > PTEs. I think this would be possible through some changes, but we can defer that > to some future work). >