linux-kernel - Re: [PATCH v3 0/4] Split page

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Message-ID: <20180301145058.GA19662@bombadil.infradead.org>
Date:   Thu, 1 Mar 2018 06:50:58 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Martin Schwidefsky <schwidefsky@...ibm.com>, linux-mm@...ck.org,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 0/4] Split page_type out from mapcount

On Thu, Mar 01, 2018 at 03:44:12PM +0300, Kirill A. Shutemov wrote:
> On Thu, Mar 01, 2018 at 08:17:50AM +0100, Martin Schwidefsky wrote:
> > Yeah, that is a nasty bit of code. On s390 we have 2K page tables (pte)
> > but 4K pages. If we use full pages for the pte tables we waste 2K of
> > memory for each of the tables. So we allocate 4K and split it into two
> > 2K pieces. Now we have to keep track of the pieces to be able to free
> > them again.
> 
> Have you considered to use slab for page table allocation instead?
> IIRC some architectures practice this already.

You're not allowed to do that any more.  Look at pgtable_page_ctor(),
or rather ptlock_init().