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From: "Li Xinhai" <lixinhai.lxh@gmail.com>
To: "linux-mm@kvack.org" <linux-mm@kvack.org>
Cc: "Mike Kravetz" <mike.kravetz@oracle.com>,
	 akpm <akpm@linux-foundation.org>
Subject: Re: [PATCH] mm/hugetlb: avoid unnecessary check on pud and pmd entry in huge_pte_offset
Date: Thu, 23 Apr 2020 21:12:23 +0800	[thread overview]
Message-ID: <202004232112215571429@gmail.com> (raw)
In-Reply-To: 1587646154-26276-1-git-send-email-lixinhai.lxh@gmail.com

On 2020-04-23 at 20:49 Li Xinhai wrote:
>When huge_pte_offset() is called, the parameter sz can only be PUD_SIZE
>or PMD_SIZE.
>If sz is PUD_SIZE and code can reach pud, then *pud must be none, or
>normal hugetlb entry, or non-present (migration or hwpoisoned) hugetlb
>entry, and we can directly return pud.
>When sz is PMD_SIZE, pud must be none or present, and if code can reach
>pmd, we can directly return pmd.
>
>So, after this patch, the code is simplified by first check on the
>parameter sz, and avoid unnecessary checks in current code.
>
>Signed-off-by: Li Xinhai <lixinhai.lxh@gmail.com>
>Cc: Mike Kravetz <mike.kravetz@oracle.com>
>Cc: Andrew Morton <akpm@linux-foundation.org> 

Since this huge_pte_offset() is under CONFIG_ARCH_WANT_GENERAL_HUGETLB, 
I only have chance to test with x86_64, but the logical should hold for all other
cases which using this general implementation.

The exsiting code path was introduced by commit 9b19df292c6 (mm/hugetlb.c:
make huge_pte_offset() consistent and document behaviour), and the sematics
is maintained after current patch applied.


  reply	other threads:[~2020-04-23 13:12 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-23 12:49 [PATCH] mm/hugetlb: avoid unnecessary check on pud and pmd entry in huge_pte_offset Li Xinhai
2020-04-23 13:12 ` Li Xinhai [this message]
2020-04-23 18:14 ` Mike Kravetz
2020-04-23 18:38   ` Jason Gunthorpe
2020-04-24  4:07     ` Li Xinhai
2020-04-24 12:57       ` Jason Gunthorpe
2020-04-24 13:33         ` Li Xinhai
2020-04-24 13:42           ` Jason Gunthorpe
2020-04-24 14:07             ` Li Xinhai
2020-04-24 14:10               ` Jason Gunthorpe
2020-04-24 14:53                 ` Li Xinhai

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