linux-kernel - Re: [PATCH 0/4] mm: Use slab_list list

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Message-ID: <20190312010554.GA9362@eros.localdomain>
Date:   Tue, 12 Mar 2019 12:05:54 +1100
From:   "Tobin C. Harding" <me@...in.cc>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Roman Gushchin <guro@...com>,
        "Tobin C. Harding" <tobin@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/4] mm: Use slab_list list_head instead of lru

On Mon, Mar 11, 2019 at 04:16:33PM -0700, Matthew Wilcox wrote:
> On Mon, Mar 11, 2019 at 08:49:23PM +0000, Roman Gushchin wrote:
> > The patchset looks good to me, however I'd add some clarifications
> > why switching from lru to slab_list is safe.
> > 
> > My understanding is that the slab_list fields isn't currently in use,
> > but it's not that obvious that putting slab_list and next/pages/pobjects
> > fields into a union is safe (for the slub case).
> 
> It's already in a union.
> 
> struct page {
>         union {
>                 struct {        /* Page cache and anonymous pages */
>                         struct list_head lru;
> ...
>                 struct {        /* slab, slob and slub */
>                         union {
>                                 struct list_head slab_list;     /* uses lru */
>                                 struct {        /* Partial pages */
>                                         struct page *next;
> 
> slab_list and lru are in the same bits.  Once this patch set is in,
> we can remove the enigmatic 'uses lru' comment that I added.

Funny you should say this, I came to me today while daydreaming that I
should have removed that comment :)

I'll remove it in v2.

thanks,
Tobin.