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

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Message-ID: <20190311231633.GF19508@bombadil.infradead.org>
Date:   Mon, 11 Mar 2019 16:16:33 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Roman Gushchin <guro@...com>
Cc:     "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 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.