linux-kernel - Re: a question about slub in function __slab

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Date:	Wed, 2 Mar 2016 23:38:44 +0900
From:	Joonsoo Kim <js1304@...il.com>
To:	Xishi Qiu <qiuxishi@...wei.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, Linux MM <linux-mm@...ck.org>
Subject: Re: a question about slub in function __slab_free()

2016-03-02 21:26 GMT+09:00 Xishi Qiu <qiuxishi@...wei.com>:
> ___slab_alloc()
>         deactivate_slab()
>                 add_full(s, n, page);
> The page will be added to full list and the frozen is 0, right?
>
> __slab_free()
>         prior = page->freelist;  // prior is NULL
>         was_frozen = new.frozen;  // was_frozen is 0
>         ...
>                 /*
>                  * Slab was on no list before and will be
>                  * partially empty
>                  * We can defer the list move and instead
>                  * freeze it.
>                  */
>                 new.frozen = 1;
>         ...
>
> I don't understand why "Slab was on no list before"?

add_full() is defined only for CONFIG_SLUB_DEBUG.
And, actual add happens if slub_debug=u is enabled.
In other cases, fully used slab isn't attached on any list.

Thanks.