linux-kernel - Re: [PATCH] mm: avoid slub allocation while holding list

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Message-Id: <201909100141.x8A1fVdu048305@www262.sakura.ne.jp>
Date:   Tue, 10 Sep 2019 10:41:31 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Yu Zhao <yuzhao@...gle.com>
Cc:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: avoid slub allocation while holding
 list_lock

Yu Zhao wrote:
> I think we can safely assume PAGE_SIZE is unsigned long aligned and
> page->objects is non-zero. But if you don't feel comfortable with these
> assumptions, I'd be happy to ensure them explicitly.

I know PAGE_SIZE is unsigned long aligned. If someone by chance happens to
change from "dynamic allocation" to "on stack", get_order() will no longer
be called and the bug will show up.

I don't know whether __get_free_page(GFP_ATOMIC) can temporarily consume more
than 4096 bytes, but if it can, we might want to avoid "dynamic allocation".

By the way, if "struct kmem_cache_node" is object which won't have many thousands
of instances, can't we embed that buffer into "struct kmem_cache_node" because
max size of that buffer is only 4096 bytes?