linux-kernel - Re: [PATCH] arch, mm: introduce arch_tlb_gather_mmu_lazy (was: Re: [RESEND PATCH] mm, oom_reaper: gather each vma to prevent) leaking TLB entry

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Message-ID: <20171113095107.24hstywywxk7nx7e@dhcp22.suse.cz>
Date:   Mon, 13 Nov 2017 10:51:07 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Wang Nan <wangnan0@...wei.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, will.deacon@....com,
        Bob Liu <liubo95@...wei.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Rientjes <rientjes@...gle.com>,
        Ingo Molnar <mingo@...nel.org>, Roman Gushchin <guro@...com>,
        Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH] arch, mm: introduce arch_tlb_gather_mmu_lazy (was: Re:
 [RESEND PATCH] mm, oom_reaper: gather each vma to prevent) leaking TLB entry

On Mon 13-11-17 09:28:33, Minchan Kim wrote:
[...]
> Thanks for the patch, Michal.
> However, it would be nice to do it tranparently without asking
> new flags from users.
> 
> When I read tlb_gather_mmu's description, fullmm is supposed to
> be used only if there is no users and full address space.
> 
> That means we can do it API itself like this?
> 
> void arch_tlb_gather_mmu(...)
> 
>         tlb->fullmm = !(start | (end + 1)) && atomic_read(&mm->mm_users) == 0;

I do not have a strong opinion here. The optimization is quite subtle so
calling it explicitly sounds like a less surprising behavior to me
longterm. Note that I haven't checked all fullmm users.

-- 
Michal Hocko
SUSE Labs