From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-98.freemail.mail.aliyun.com (out30-98.freemail.mail.aliyun.com [115.124.30.98]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1C7A55478D for ; Wed, 17 Dec 2025 02:03:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.98 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765937027; cv=none; b=WPnbucFBInJ3ya8X/TxIVJka1kvKFe1ZkK3NIqCQdLYaCEKpperoZ8kekifd0P7FfvWCFvIsydXvYyDfIMW2yRFi9UhE+ey3QZUrUyN27BxMqmmH26Uz4U0XqDe6KORvKQjGlECa0VUZfuPWA2mwesPW6aY8egSF/leCrVKPytU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765937027; c=relaxed/simple; bh=hf19NawRm9agCbFLlFe+8GMsqA+54jxNPFT9tBgSWLU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Vk5tRA6iRFoIEURm2+O32eK+lZhBvc2/J2rBjusSSN9UHf9kcDYh+pHUmgY1L4qXJ0B5KZ6Ktbq8gAVYiXyrlYZlC2sLEk/AOKgg3JVPg3ZdHTZ0jMwkdb/FnMTSafW9a+IwDPZFGGzG7gxWkih3zNULa2ABKxMSiV5TsFyT/n0= ARC-Authentication-Results:i=1; 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Wed, 17 Dec 2025 10:03:40 +0800 Message-ID: <324b64d3-2d12-462c-9afc-070dd100c582@linux.alibaba.com> Date: Wed, 17 Dec 2025 10:03:38 +0800 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 07/11] mm: shmem: use pgtable_has_pmd_leaves() To: Luiz Capitulino , linux-kernel@vger.kernel.org, linux-mm@kvack.org, david@kernel.org Cc: ryan.roberts@arm.com, akpm@linux-foundation.org, lorenzo.stoakes@oracle.com References: <64b1e5fd-113d-4874-9b6c-6e344bd24ed5@redhat.com> From: Baolin Wang In-Reply-To: <64b1e5fd-113d-4874-9b6c-6e344bd24ed5@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 2025/12/16 21:47, Luiz Capitulino wrote: > On 2025-12-16 02:52, Baolin Wang wrote: >> >> >> On 2025/12/16 05:16, Luiz Capitulino wrote: >>> Shmem uses has_transparent_hugepage() to check if PMD-sized pages are >>> supported, use pgtable_has_pmd_leaves() instead. >>> >>> Signed-off-by: Luiz Capitulino >>> --- >>>   mm/shmem.c | 7 ++++--- >>>   1 file changed, 4 insertions(+), 3 deletions(-) >>> >>> diff --git a/mm/shmem.c b/mm/shmem.c >>> index b329b5302c48..ad5825667b49 100644 >>> --- a/mm/shmem.c >>> +++ b/mm/shmem.c >>> @@ -689,7 +689,8 @@ static int shmem_parse_huge(const char *str) >>>       else >>>           return -EINVAL; >>> -    if (!has_transparent_hugepage() && >>> +    if (!(IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && >>> +          pgtable_has_pmd_leaves()) && >>>           huge != SHMEM_HUGE_NEVER && huge != SHMEM_HUGE_DENY) >>>           return -EINVAL; >>> @@ -4655,7 +4656,7 @@ static int shmem_parse_one(struct fs_context >>> *fc, struct fs_parameter *param) >>>           ctx->huge = result.uint_32; >>>           if (ctx->huge != SHMEM_HUGE_NEVER && >>>               !(IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && >>> -              has_transparent_hugepage())) >>> +              pgtable_has_pmd_leaves())) >>>               goto unsupported_parameter; >>>           ctx->seen |= SHMEM_SEEN_HUGE; >>>           break; >>> @@ -5439,7 +5440,7 @@ void __init shmem_init(void) >>>   #endif >>>   #ifdef CONFIG_TRANSPARENT_HUGEPAGE >>> -    if (has_transparent_hugepage() && shmem_huge > SHMEM_HUGE_DENY) >>> +    if (pgtable_has_pmd_leaves() && shmem_huge > SHMEM_HUGE_DENY) >> >> Using pgtable_has_pmd_leaves() here is a bit confusing because the >> definition of pgtable_has_pmd_leaves() is: it returns true if the CPU >> supports PMD-sized pages and false otherwise. >> >> However, tmpfs and shmem already support other sizes of large folios, >> not just PMD-sized large folios. >> >> So, for me, using has_transparent_hugepage() to check would be at >> least clearer (even though it doesn't change the functionality). > > This is more of a naming issue, correct? Yes. > Would adding something like thp_has_pmd_support() which expands to: > >     return IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && > pgtable_has_pmd_leaves(); > > solve it for you? I suggested it in my RFC, but David advised not to do it. I agree with David. The thp_has_pmd_support() is not helpful too. What I mean is that the term 'pmd' shouldn't be used here. PMD-sized large folios aren't any more special than others. shmem also supports mTHP, and a better approach might be what you did in patch 10: even if PMD-sized pages are not supported on an architecture, shmem can still use other sizes of mTHP. > Also, I'm not sure if the comparison with other folio sizes apply, as > PUD and PMD sizes are special.