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

From: Michal Hocko <mhocko@kernel.org>
To: Minchan Kim <minchan@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	will.deacon@arm.com, Bob Liu <liubo95@huawei.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	David Rientjes <rientjes@google.com>,
	Ingo Molnar <mingo@kernel.org>, Roman Gushchin <guro@fb.com>,
	Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
	Andrea Arcangeli <aarcange@redhat.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
Date: Mon, 13 Nov 2017 10:51:07 +0100	[thread overview]
Message-ID: <20171113095107.24hstywywxk7nx7e@dhcp22.suse.cz> (raw)
In-Reply-To: <20171113002833.GA18301@bbox>

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