linux-kernel - Re: [PATCH uprobe, thp 4/4] uprobe: collapse THP pmd after removing all uprobes

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Message-ID: <20190530122055.xzlbo3wfpqtmo2fw@box>
Date:   Thu, 30 May 2019 15:20:55 +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 4/4] uprobe: collapse THP pmd after removing
 all uprobes

On Wed, May 29, 2019 at 02:20:49PM -0700, Song Liu wrote:
> After all uprobes are removed from the huge page (with PTE pgtable), it
> is possible to collapse the pmd and benefit from THP again. This patch
> does the collapse.

I don't think it's right way to go. We should deferred it to khugepaged.
We need to teach khugepaged to deal with PTE-mapped compound page.
And uprobe should only kick khugepaged for a VMA. Maybe synchronously.

-- 
 Kirill A. Shutemov