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

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Message-ID: <20190621133613.xnzpdlicqvjklrze@box>
Date:   Fri, 21 Jun 2019 16:36:13 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Song Liu <songliubraving@...com>
Cc:     LKML <linux-kernel@...r.kernel.org>, Linux-MM <linux-mm@...ck.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>
Subject: Re: [PATCH v4 5/5] uprobe: collapse THP pmd after removing all
 uprobes

On Fri, Jun 21, 2019 at 01:17:05PM +0000, Song Liu wrote:
> 
> 
> > On Jun 21, 2019, at 5:48 AM, Kirill A. Shutemov <kirill@...temov.name> wrote:
> > 
> > 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).
> > 
> 
> I see the point now. I misunderstood it for a while. 
> 
> If we add this to khugepaged, it will have some conflicts with my other 
> patchset. How about we move the functionality to khugepaged after these
> two sets get in? 

Is the last patch of the patchset essential? I think this part can be done
a bit later in a proper way, no?

-- 
 Kirill A. Shutemov