linux-kernel - Re: [RFC v9 PATCH 2/4] mm: mmap: zap pages with read mmap

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Date:   Wed, 12 Sep 2018 11:11:05 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Yang Shi <yang.shi@...ux.alibaba.com>, ldufour@...ux.vnet.ibm.com,
        vbabka@...e.cz, akpm@...ux-foundation.org, dave.hansen@...el.com,
        oleg@...hat.com, srikar@...ux.vnet.ibm.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC v9 PATCH 2/4] mm: mmap: zap pages with read mmap_sem in
 munmap

On Tue 11-09-18 19:29:21, Matthew Wilcox wrote:
> On Tue, Sep 11, 2018 at 04:35:03PM -0700, Yang Shi wrote:
[...]

I didn't get to read the patch yet.

> > And, Michal prefers have VM_HUGETLB and VM_PFNMAP handled separately for
> > safe and bisectable sake, which needs call the regular do_munmap().
> 
> That can be introduced and then taken out ... indeed, you can split this into
> many patches, starting with this:
> 
> +		if (tmp->vm_file)
> +			downgrade = false;
> 
> to only allow this optimisation for anonymous mappings at first.

or add a helper function to check for special cases and make the
downgrade behavior conditional on it.
-- 
Michal Hocko
SUSE Labs