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Tue, 22 Sep 2026 18:37:55 -0700 (PDT) Message-ID: <3d914185-ac87-4fc7-ab21-de184bfd4e57@redhat.com> Date: Tue, 22 Sep 2026 21:37:53 -0400 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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: Zi Yan , linux-kernel@vger.kernel.org, linux-mm@kvack.org, david@kernel.org, baolin.wang@linux.alibaba.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: Content-Language: en-US From: Luiz Capitulino In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 9/21/26 10:20 PM, Zi Yan wrote: > On Thu Sep 17, 2026 at 9:45 PM EDT, 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; > > This can be deleted, since shmem_parse_huge() is guarded by > CONFIG_TRANSPARENT_HUGEPAGE and after the change the if is always false > under that guard. > > Otherwise, LGTM. With the above code deleted, feel free to add > > Reviewed-by: Zi Yan OK, here's the diff: diff --git a/mm/shmem.c b/mm/shmem.c index c00bc1829fc9..d12995d41846 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -690,10 +690,6 @@ static int shmem_parse_huge(const char *str) else return -EINVAL; - if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && - huge != SHMEM_HUGE_NEVER && huge != SHMEM_HUGE_DENY) - return -EINVAL; - /* Do not override huge allocation policy with non-PMD sized mTHP */ if (huge == SHMEM_HUGE_FORCE && huge_shmem_orders_inherit != BIT(HPAGE_PMD_ORDER))