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

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Message-ID: <20190530121400.amti2s5ilrba2wvb@box>
Date:   Thu, 30 May 2019 15:14:00 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Song Liu <songliubraving@...com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org, namit@...are.com,
        peterz@...radead.org, oleg@...hat.com, rostedt@...dmis.org,
        mhiramat@...nel.org, matthew.wilcox@...cle.com,
        kirill.shutemov@...ux.intel.com, kernel-team@...com,
        william.kucharski@...cle.com, chad.mynhier@...cle.com,
        mike.kravetz@...cle.com
Subject: Re: [PATCH uprobe, thp 3/4] uprobe: support huge page by only
 splitting the pmd

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()?

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

-- 
 Kirill A. Shutemov