linux-kernel - Re: [PATCH 1/2] mm: slab/slub: use page->list consistently instead of page->lru

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Message-ID: <alpine.DEB.2.02.1312111443130.7354@chino.kir.corp.google.com>
Date:	Wed, 11 Dec 2013 14:45:23 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Dave Hansen <dave@...1.net>
cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org, cl@...two.org,
	kirill.shutemov@...ux.intel.com, Andi Kleen <ak@...ux.intel.com>,
	akpm@...ux-foundation.org
Subject: Re: [PATCH 1/2] mm: slab/slub: use page->list consistently instead
 of page->lru

On Wed, 11 Dec 2013, Dave Hansen wrote:

> From: Dave Hansen <dave.hansen@...ux.intel.com>
> 
> 'struct page' has two list_head fields: 'lru' and 'list'.
> Conveniently, they are unioned together.  This means that code
> can use them interchangably, which gets horribly confusing like
> with this nugget from slab.c:
> 
> >	list_del(&page->lru);
> >	if (page->active == cachep->num)
> >		list_add(&page->list, &n->slabs_full);
> 
> This patch makes the slab and slub code use page->list
> universally instead of mixing ->list and ->lru.
> 
> It also adds some comments to attempt to keep new users from
> picking up uses of ->list.
> 
> So, the new rule is: page->list is what the slabs use.  page->lru
> is for everybody else.  This is a pretty arbitrary rule, but we
> need _something_.  Maybe we should just axe the ->list one and
> make the sl?bs use ->lru.
> 

I'd recommend this suggestion, I don't see why the slab allocators can't 
use a page->lru field to maintain their lists of slab pages and it makes 
the code much cleaner.  Anybody hacking thise code will know it's not 
really a lru and we're just reusing a field from struct page without 
adding unnecessary complexity.
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