From: "H. Peter Anvin" <hpa@zytor.com>
To: Dave Hansen <dave@sr71.net>
Cc: tglx@linutronix.de, mingo@redhat.com, x86@kernel.org,
peterz@infradead.org, bp@alien8.de, luto@amacapital.net,
torvalds@linux-foundation.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC][PATCH] x86, fpu: dynamically allocate 'struct fpu'
Date: Thu, 16 Jul 2015 15:42:24 -0700 [thread overview]
Message-ID: <55A83350.1080603@zytor.com> (raw)
In-Reply-To: <20150716191437.A334FF2E@viggo.jf.intel.com>
On 07/16/2015 12:14 PM, Dave Hansen wrote:
> The FPU rewrite removed the dynamic allocations of 'struct fpu'.
> But, this potentially wastes massive amounts of memory (2k per
> task on systems that do not have AVX-512 for instance).
>
> Instead of having a separate slab, this patch just appends the
> space that we need to the 'task_struct' which we dynamically
> allocate already. This saves from doing an extra slab allocation
> at fork(). The only real downside here is that we have to stick
> everything and the end of the task_struct. But, I think the
> BUILD_BUG_ON()s I stuck in there should keep that from being too
> fragile.
>
> This survives a quick build and boot in a VM. Does anyone see any
> real downsides to this?
>
No. I have also long advocated for merging task_struct and thread_info
into a common structure and get it off the stack; it would improve
security and avoid weird corner cases in the irqstack handling.
-hpa
next prev parent reply other threads:[~2015-07-16 22:43 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-16 19:14 [RFC][PATCH] x86, fpu: dynamically allocate 'struct fpu' Dave Hansen
2015-07-16 19:25 ` Andy Lutomirski
2015-07-16 21:29 ` Dave Hansen
2015-07-17 8:45 ` Ingo Molnar
2015-07-17 9:31 ` [PATCH] x86/fpu, sched: Introduce CONFIG_ARCH_WANTS_DYNAMIC_TASK_STRUCT and use it on x86 Ingo Molnar
2015-07-16 22:35 ` [RFC][PATCH] x86, fpu: dynamically allocate 'struct fpu' Peter Zijlstra
2015-07-17 8:39 ` Ingo Molnar
2015-07-17 8:43 ` [PATCH] x86/fpu, bug.h: Move CHECK_MEMBER_AT_END_OF() to a generic header and use it in generic code Ingo Molnar
2015-07-16 22:42 ` H. Peter Anvin [this message]
2015-07-16 22:57 ` [RFC][PATCH] x86, fpu: dynamically allocate 'struct fpu' Andy Lutomirski
2015-07-18 3:40 ` Ingo Molnar
2015-07-17 8:23 ` Ingo Molnar
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