linux-kernel - Re: [PATCH uprobe, thp 3/4] uprobe: support huge page by only splitting the pmd

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Message-ID: <2BF5CB81-166B-45E8-908A-CF5EDAEC05D1@fb.com>
Date:   Thu, 30 May 2019 17:37:03 +0000
From:   Song Liu <songliubraving@...com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
CC:     LKML <linux-kernel@...r.kernel.org>, Linux-MM <linux-mm@...ck.org>,
        "namit@...are.com" <namit@...are.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "oleg@...hat.com" <oleg@...hat.com>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "mhiramat@...nel.org" <mhiramat@...nel.org>,
        "matthew.wilcox@...cle.com" <matthew.wilcox@...cle.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        Kernel Team <Kernel-team@...com>,
        "william.kucharski@...cle.com" <william.kucharski@...cle.com>,
        "chad.mynhier@...cle.com" <chad.mynhier@...cle.com>,
        "mike.kravetz@...cle.com" <mike.kravetz@...cle.com>
Subject: Re: [PATCH uprobe, thp 3/4] uprobe: support huge page by only
 splitting the pmd



> On May 30, 2019, at 5:14 AM, Kirill A. Shutemov <kirill@...temov.name> wrote:
> 
> On Wed, May 29, 2019 at 02:20:48PM -0700, Song Liu wrote:
>> Instead of splitting the compound page with FOLL_SPLIT, this patch allows
>> uprobe to only split pmd for huge pages.
>> 
>> A helper function mm_address_trans_huge(mm, address) was introduced to
>> test whether the address in mm is pointing to THP.
> 
> Maybe it would be cleaner to have FOLL_SPLIT_PMD which would strip
> trans_huge PMD if any and then set pte using get_locked_pte()?

FOLL_SPLIT_PMD sounds like a great idea! Let me try it. 

Thanks,
Song

> 
> This way you'll not need any changes in split_huge_pmd() path. Clearing
> PMD will be fine.
> 
> -- 
> Kirill A. Shutemov