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

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Message-ID: <4E8A7A5E-D425-40EC-B40A-7DA21BA1866F@fb.com>
Date:   Thu, 30 May 2019 17:26:38 +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 4/4] uprobe: collapse THP pmd after removing
 all uprobes



> On May 30, 2019, at 5:20 AM, Kirill A. Shutemov <kirill@...temov.name> wrote:
> 
> 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.
> 

I guess that would be the same logic, but run in khugepaged? It doesn't
have to be done synchronously. 

Let me try that

Thanks,
Song


> -- 
> Kirill A. Shutemov