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Message-ID: <alpine.LFD.1.00.0803291422160.14670@woody.linux-foundation.org>
Date: Sat, 29 Mar 2008 14:29:27 -0700 (PDT)
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Christoph Lameter <clameter@....com>
cc: "Rafael J. Wysocki" <rjw@...k.pl>,
Pawel Staszewski <pstaszewski@...com.pl>,
LKML <linux-kernel@...r.kernel.org>,
Adrian Bunk <bunk@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Natalie Protasevich <protasnb@...il.com>
Subject: Re: 2.6.25-rc7-git2: Reported regressions from 2.6.24
On Sat, 29 Mar 2008, Christoph Lameter wrote:
>
> > If SLUB *ever* calls the page allocator with __GFP_ZERO set, it's a
> > bug, and that has nothing to do with GFP_ATOMIC or anything else. Because
> > SLUB uses its own logic for clearing the result.
>
> Yes it uses its own logic if the object is managed by SLUB but not if the
> object is too big and/or the allocation forwarded to the page allocator
> or for other internal allocations of buffers etc.
Wrong.
It uses it's own logic for __GFP_ZERO *regardless* of size.
> > Why cannot you just admit it?
>
> Admitting something that is not true is rather difficult.
You don't have a f*cking clue about this cocde that you're supposed to be
maintaining, do you?
See "slab_alloc()". See the code:
if (unlikely((gfpflags & __GFP_ZERO) && object))
memset(object, 0, c->objsize);
and see how it does it regardless of anything else.
In short, if *any* code-path calls down to any allocator from that routine
with GFP_ZERO set, it's a bug. No ifs, buts or maybes about it. It
shouldn't do that, because the actual memset() is done by slab_alloc(),
and should not be done ANYWHERE ELSE.
It has *nothing* to do with "object is too big" or anything else.
> So what you want is to forbid any use of
>
> alloc_pages(__GFP_ZERO|...)
No. I want you to admit the bugs in code you maintain. I want you to admit
that slab_alloc() does the memset(), and should NEVER EVER use __GFP_ZERO
for the page allocations.
I have told you about a million times now that THIS HAS NOTHING TO DO WITH
interrupts or HIGHMEM or *anything* else. This is purely a SLUB issue.
But don't worry. I already fixed it by reverting your broken commit. I
just wish you could follow code that you are supposed to be maintaining.
Linus
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