linux-kernel - RE: amusing SLUB compaction bug when CC_OPTIMIZE_FOR

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Date:   Thu, 29 Sep 2022 11:53:17 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Hugh Dickins' <hughd@...gle.com>, Vlastimil Babka <vbabka@...e.cz>
CC:     Joel Fernandes <joel@...lfernandes.org>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: RE: amusing SLUB compaction bug when CC_OPTIMIZE_FOR_SIZE

> -static void rcu_free_slab(struct rcu_head *h)
> +/*
> + * rcu_free_slab() must be __aligned(4) because its address is saved
> + * in the rcu_head field, which coincides with page->mapping, which
> + * causes trouble if compaction mistakes it for PAGE_MAPPING_MOVABLE.
> + */
> +__aligned(4) static void rcu_free_slab(struct rcu_head *h)
>  {
>  	struct slab *slab = container_of(h, struct slab, rcu_head);
> 

Isn't that going to cause grief with options that align
functions on 16/32byte boundaries when adding space for
'other stuff'?

	David

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