linux-kernel - Re: [PATCH v4 5/5] uprobe: collapse THP pmd after removing all uprobes

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Date:   Fri, 21 Jun 2019 15:48:23 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Song Liu <songliubraving@...com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org, oleg@...hat.com,
        rostedt@...dmis.org, mhiramat@...nel.org,
        matthew.wilcox@...cle.com, kirill.shutemov@...ux.intel.com,
        kernel-team@...com
Subject: Re: [PATCH v4 5/5] uprobe: collapse THP pmd after removing all
 uprobes

On Thu, Jun 13, 2019 at 10:57:47AM -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.
> 
> An issue on earlier version was discovered by kbuild test robot.
> 
> Reported-by: kbuild test robot <lkp@...el.com>
> Signed-off-by: Song Liu <songliubraving@...com>
> ---
>  include/linux/huge_mm.h |  7 +++++
>  kernel/events/uprobes.c |  5 ++-
>  mm/huge_memory.c        | 69 +++++++++++++++++++++++++++++++++++++++++

I still sync it's duplication of khugepaged functinallity. We need to fix
khugepaged to handle SCAN_PAGE_COMPOUND and probably refactor the code to
be able to call for collapse of particular range if we have all locks
taken (as we do in uprobe case).

-- 
 Kirill A. Shutemov