linux-kernel - Re: [PATCH v4 0/3] mm, treewide: Rename kzfree() to kfree

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Message-ID: <20200616211455.GB8681@bombadil.infradead.org>
Date:   Tue, 16 Jun 2020 14:14:55 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Joe Perches <joe@...ches.com>
Cc:     Waiman Long <longman@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Howells <dhowells@...hat.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        David Rientjes <rientjes@...gle.com>,
        Michal Hocko <mhocko@...e.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        David Sterba <dsterba@...e.cz>,
        "Jason A . Donenfeld" <Jason@...c4.com>, linux-mm@...ck.org,
        keyrings@...r.kernel.org, linux-kernel@...r.kernel.org,
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Subject: Re: [PATCH v4 0/3] mm, treewide: Rename kzfree() to kfree_sensitive()

On Tue, Jun 16, 2020 at 11:53:50AM -0700, Joe Perches wrote:
> To this larger audience and last week without reply:
> https://lore.kernel.org/lkml/573b3fbd5927c643920e1364230c296b23e7584d.camel@perches.com/
> 
> Are there _any_ fastpath uses of kfree or vfree?

I worked on adding a 'free' a couple of years ago.  That was capable
of freeing percpu, vmalloc, kmalloc and alloc_pages memory.  I ran into
trouble when I tried to free kmem_cache_alloc memory -- it works for slab
and slub, but not slob (because slob needs the size from the kmem_cache).

My motivation for this was to change kfree_rcu() to just free_rcu().

> To eliminate these mispairings at a runtime cost of four
> comparisons, should the kfree/vfree/kvfree/kfree_const
> functions be consolidated into a single kfree?

I would say to leave kfree() alone and just introduce free() as a new
default.  There's some weird places in the kernel that have a 'free'
symbol of their own, but those should be renamed anyway.