linux-kernel - Re: [PATCH] mm: Fix comment for NODEMASK

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20180820142440.1f9ccbebefc5d617c881b41e@linux-foundation.org>
Date:   Mon, 20 Aug 2018 14:24:40 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Oscar Salvador <osalvador@...hadventures.net>
Cc:     tglx@...utronix.de, joe@...ches.com, arnd@...db.de,
        mhocko@...e.com, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Oscar Salvador <osalvador@...e.de>
Subject: Re: [PATCH] mm: Fix comment for NODEMASK_ALLOC

On Mon, 20 Aug 2018 10:55:16 +0200 Oscar Salvador <osalvador@...hadventures.net> wrote:

> From: Oscar Salvador <osalvador@...e.de>
> 
> Currently, NODEMASK_ALLOC allocates a nodemask_t with kmalloc when
> NODES_SHIFT is higher than 8, otherwise it declares it within the stack.
> 
> The comment says that the reasoning behind this, is that nodemask_t will be
> 256 bytes when NODES_SHIFT is higher than 8, but this is not true.
> For example, NODES_SHIFT = 9 will give us a 64 bytes nodemask_t.
> Let us fix up the comment for that.
> 
> Another thing is that it might make sense to let values lower than 128bytes
> be allocated in the stack.
> Although this all depends on the depth of the stack
> (and this changes from function to function), I think that 64 bytes
> is something we can easily afford.
> So we could even bump the limit by 1 (from > 8 to > 9).
> 

I agree.  Such a change will reduce the amount of testing which the
kmalloc version receives, but I assume there are enough people out
there testing with large NODES_SHIFT values.

And while we're looking at this, it would be nice to make NODES_SHIFT
go away.  Ensure that CONFIG_NODES_SHIFT always has a setting and use
that directly.