linux-kernel - Re: [PATCH 3/6] struct page: add field for vm

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Message-ID: <cef01110-dc23-4442-f277-88d1d3662e00@huawei.com>
Date:   Mon, 12 Feb 2018 18:24:20 +0200
From:   Igor Stoppa <igor.stoppa@...wei.com>
To:     Matthew Wilcox <willy@...radead.org>
CC:     <rdunlap@...radead.org>, <corbet@....net>, <keescook@...omium.org>,
        <mhocko@...nel.org>, <labbott@...hat.com>, <jglisse@...hat.com>,
        <hch@...radead.org>, <cl@...ux.com>,
        <linux-security-module@...r.kernel.org>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>,
        <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH 3/6] struct page: add field for vm_struct



On 11/02/18 23:16, Matthew Wilcox wrote:
> On Sun, Feb 11, 2018 at 05:19:17AM +0200, Igor Stoppa wrote:
>> The struct page has a "mapping" field, which can be re-used, to store a
>> pointer to the parent area. This will avoid more expensive searches.
>>
>> As example, the function find_vm_area is reimplemented, to take advantage
>> of the newly introduced field.
> 
> Umm.  Is it more efficient?  You're replacing an rb-tree search with a
> page-table walk.  You eliminate a spinlock, which is great, but is the
> page-table walk more efficient?  I suppose it'll depend on the depth of
> the rb-tree, and (at least on x86), the page tables should already be
> in cache.

I thought the tradeoff favorable. How to verify it?

> Unrelated to this patch, I'm working on a patch to give us page_type,
> and I think I'll allocate a bit to mark pages which are vmalloced.

pmalloced too?

--
igor