From: Andrew Morton <akpm@linux-foundation.org>
To: Michal Hocko <mhocko@kernel.org>
Cc: Yang Shi <yang.shi@linux.alibaba.com>,
willy@infradead.org, ldufour@linux.vnet.ibm.com,
kirill@shutemov.name, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [RFC v4 0/3] mm: zap pages with read mmap_sem in munmap for large mapping
Date: Wed, 11 Jul 2018 15:49:54 -0700 [thread overview]
Message-ID: <20180711154954.afe001e284574cd5d4c3ec89@linux-foundation.org> (raw)
In-Reply-To: <20180711103312.GH20050@dhcp22.suse.cz>
On Wed, 11 Jul 2018 12:33:12 +0200 Michal Hocko <mhocko@kernel.org> wrote:
> > Approach:
> > Zapping pages is the most time consuming part, according to the suggestion from
> > Michal Hocko [1], zapping pages can be done with holding read mmap_sem, like
> > what MADV_DONTNEED does. Then re-acquire write mmap_sem to cleanup vmas.
> >
> > But, we can't call MADV_DONTNEED directly, since there are two major drawbacks:
> > * The unexpected state from PF if it wins the race in the middle of munmap.
> > It may return zero page, instead of the content or SIGSEGV.
> > * Can’t handle VM_LOCKED | VM_HUGETLB | VM_PFNMAP and uprobe mappings, which
> > is a showstopper from akpm
>
> I do not really understand why this is a showstopper. This is a mere
> optimization. VM_LOCKED ranges are usually not that large. VM_HUGETLB
> can be quite large alright but this should be doable on top. Is there
> any reason to block any "cover most mappings first" patch?
Somebody somewhere is going to want to unmap vast mlocked regions and
they're going to report softlockup warnings. So we shouldn't implement
something which can't address these cases. Maybe it doesn't do so in
the first version, but we should at least have a plan to handle all
cases.
WARNING: multiple messages have this Message-ID (diff)
From: Andrew Morton <akpm@linux-foundation.org>
To: Michal Hocko <mhocko@kernel.org>
Cc: Yang Shi <yang.shi@linux.alibaba.com>,
willy@infradead.org, ldufour@linux.vnet.ibm.com,
kirill@shutemov.name, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [RFC v4 0/3] mm: zap pages with read mmap_sem in munmap for large mapping
Date: Wed, 11 Jul 2018 15:49:54 -0700 [thread overview]
Message-ID: <20180711154954.afe001e284574cd5d4c3ec89@linux-foundation.org> (raw)
In-Reply-To: <20180711103312.GH20050@dhcp22.suse.cz>
On Wed, 11 Jul 2018 12:33:12 +0200 Michal Hocko <mhocko@kernel.org> wrote:
> > Approach:
> > Zapping pages is the most time consuming part, according to the suggestion from
> > Michal Hocko [1], zapping pages can be done with holding read mmap_sem, like
> > what MADV_DONTNEED does. Then re-acquire write mmap_sem to cleanup vmas.
> >
> > But, we can't call MADV_DONTNEED directly, since there are two major drawbacks:
> > * The unexpected state from PF if it wins the race in the middle of munmap.
> > It may return zero page, instead of the content or SIGSEGV.
> > * Cana??t handle VM_LOCKED | VM_HUGETLB | VM_PFNMAP and uprobe mappings, which
> > is a showstopper from akpm
>
> I do not really understand why this is a showstopper. This is a mere
> optimization. VM_LOCKED ranges are usually not that large. VM_HUGETLB
> can be quite large alright but this should be doable on top. Is there
> any reason to block any "cover most mappings first" patch?
Somebody somewhere is going to want to unmap vast mlocked regions and
they're going to report softlockup warnings. So we shouldn't implement
something which can't address these cases. Maybe it doesn't do so in
the first version, but we should at least have a plan to handle all
cases.
next prev parent reply other threads:[~2018-07-11 22:49 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-10 23:34 [RFC v4 0/3] mm: zap pages with read mmap_sem in munmap for large mapping Yang Shi
2018-07-10 23:34 ` Yang Shi
2018-07-10 23:34 ` [RFC v4 PATCH 1/3] mm: introduce VM_DEAD flag and extend check_stable_address_space to check it Yang Shi
2018-07-10 23:34 ` [RFC v4 PATCH 2/3] mm: refactor do_munmap() to extract the common part Yang Shi
2018-07-10 23:34 ` [RFC v4 PATCH 3/3] mm: mmap: zap pages with read mmap_sem for large mapping Yang Shi
2018-07-11 10:33 ` [RFC v4 0/3] mm: zap pages with read mmap_sem in munmap " Michal Hocko
2018-07-11 10:33 ` Michal Hocko
2018-07-11 11:13 ` Kirill A. Shutemov
2018-07-11 11:53 ` Michal Hocko
2018-07-11 17:08 ` Yang Shi
2018-07-11 16:57 ` Yang Shi
2018-07-11 16:57 ` Yang Shi
2018-07-11 22:49 ` Andrew Morton [this message]
2018-07-11 22:49 ` Andrew Morton
2018-07-12 8:15 ` Michal Hocko
2018-07-12 8:15 ` Michal Hocko
2018-07-11 11:10 ` Kirill A. Shutemov
2018-07-11 11:10 ` Kirill A. Shutemov
2018-07-11 11:58 ` Michal Hocko
2018-07-11 17:04 ` Yang Shi
2018-07-11 17:04 ` Yang Shi
2018-07-12 8:04 ` Michal Hocko
2018-07-12 23:45 ` Yang Shi
2018-07-12 23:45 ` Yang Shi
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