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b=BGSX/Kbts2HyomUYIll1ZSW1Dc6xBceYErF3oCIvBLGsnn+9W/iL8dUWzD10Xxshv ZN83CvovSLCevLrxWllAASgTHRUTKqmEDI8r3B61oraf+GBHIM9rlNJra3/KUEcZwc Gj3mYj5JVSkng+Z1vgJR2AZoiHbPmGwRvgg3WWugxxYNsWyLXNycxtqZyemtlKslJv Xr3zyVh84R34zkPGPo3zG7qHoDMJZ6WRceBLfPeQHeWmJJ2QYxjRNGKEp5Z65cWpBM UoaqMSQstAgxR6XPvPEi1TRTfgUaDiaxDCVp7Kq3iHcgWMIx1HNSyd6TRyX8eGGm+w vWH/q2umXu0wQ== Message-ID: Date: Fri, 2 Oct 2026 21:23:54 +0200 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: Luiz Capitulino , 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: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: o8souub4xk1jii6wa1dec9xnqxgysrbz X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: A0C8820008 X-HE-Tag: 1790969045-647688 X-HE-Meta: U2FsdGVkX1+MtFcf8bAZaoSmL97D4q/rigjQ8Db8fEPUT+Qyk2WTHwGUlisw5BP2QWO6RNjqDFSuGbHjk31lJUCzigw7Rn1DtayOt/W4Q7PODdEvClLbkuFgbZCxRCio88gujG86zo7ubW616kLcEXZ8P2xcpxeRFi3G27dJfDcR0NhW0YfTlk61Laj59bRPwmirQcEKOhuAIj/Yrw5Z3EYg7HIHtCNFwIQn8S3886f5Za9QnSKho5gZhIle7xOeRNhgHL/+oEVFru7XZR33qApBE4UxeLAJwc1CsEvIh8r7/w3THOTadoholxNIIzwsPO5Pqek6hHg+gE4egiR+8lNZTT+DiSWNMsukTEmAha2UBY8T76VXI7twNyGG2RdveOJNYOHcaz1NG+fOmIdhmHtYNfrb5Vh0wcFgXJXevCou2Qb8F5K7qXDHynVUWVonRMEEoUWfiuhypWSX/37cSyZP+E6caFfTlk1MRTWJE6qI/UHd/SQja3j+UwabYvUIIrNaH5a5wKPk1CSNOnMxmPYPrgsCghSnWPNsSsAsswIzXIwVN3AD+FkqnTvhICc6X9Ycy/1AxHnaRueYqzz50cP6rvzAWDbd59x+B4wtZkwY7QAyk8EbWKD9A/CzhoLxk3fNXPwIh+G6lfY716GzH44rB4uzjxcsAfaacMvjc41JGCF4GkDbvGMNBPoHIUz25yrAUNNx8f7L5GYvRlIJMk2+ktFELlvyeoqRm7cE3BeG+X7LMpY7iDGJPFEJ11DtZUCp2YHU6TnfrKMG5M5VhbtVNuJUjIYdntLoCCK7es+/3y4gP4YKGsHzDIdGhcCh8jtkjdq5gdiqGq627lYo7ImLvE5cuJJFVkd2DfxfQCrAd87oYKiVXg6JDphYJdLDXHgKfr1hcvzYGKpSGRxAR6yXurH9IJz6XwHmMiw0rHQ+Tr9bRWAYziUzEcbwmGa0749CYFt99mHorsgvEeC 3BabcJ9a AA4f6/t7l0IjS/2gesIlAFXzle0nIO5JzQEVy0oJ+QAskvqzsnc0NEQvPHM7B3EINpJKM013lt2owlAbSnKu86Bnbuwi+EY5CcQZV3DEo3E4k3/Y8nSKUUnrNwa6T1Ww9p5Wf3yAur3UaMfKdP0YyJ6IwTct//YEDQ9gzPrdwZ34QSqFNZlAAd2RK4G0y8BdeGDqykahA5ki2V3ZDnzUGSJrVz5obBRLsBvZx9j6krXaU4De1y8KLuPMyG2HN0a40QtGfYBjLO9u+oGMarARyw8wia8TQyYVW/XloSVywE7XwfCElpQI0H6uLWw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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". (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). -- Cheers, David