|From:||Linus Torvalds <torvalds-AT-linux-foundation.org>|
|To:||Dave Chinner <david-AT-fromorbit.com>|
|Subject:||Re: [RFC 2/2] x86_64: expand kernel stack to 16K|
|Date:||Thu, 29 May 2014 08:24:49 -0700|
|Cc:||Jens Axboe <axboe-AT-kernel.dk>, Minchan Kim <minchan-AT-kernel.org>, Linux Kernel Mailing List <linux-kernel-AT-vger.kernel.org>, Andrew Morton <akpm-AT-linux-foundation.org>, linux-mm <linux-mm-AT-kvack.org>, "H. Peter Anvin" <hpa-AT-zytor.com>, Ingo Molnar <mingo-AT-kernel.org>, Peter Zijlstra <a.p.zijlstra-AT-chello.nl>, Mel Gorman <mgorman-AT-suse.de>, Rik van Riel <riel-AT-redhat.com>, Johannes Weiner <hannes-AT-cmpxchg.org>, Hugh Dickins <hughd-AT-google.com>, Rusty Russell <rusty-AT-rustcorp.com.au>, "Michael S. Tsirkin" <mst-AT-redhat.com>, Dave Hansen <dave.hansen-AT-intel.com>, Steven Rostedt <rostedt-AT-goodmis.org>|
On Thu, May 29, 2014 at 12:26 AM, Dave Chinner <email@example.com> wrote: > > What concerns me about both __alloc_pages_nodemask() and > kernel_map_pages is that when I look at the code I see functions > that have no obvious stack usage problem. However, the compiler is > producing functions with huge stack footprints and it's not at all > obvious when I read the code. So in this case I'm more concerned > that we have a major disconnect between the source code structure > and the code that the compiler produces... I agree. In fact, this is the main reason that Minchan's call trace and this thread has actually convinced me that yes, we really do need to make x86-64 have a 16kB stack (well, 16kB allocation - there's still the thread info etc too). Usually when we see the stack-smashing traces, they are because somebody did something stupid. In this case, there are certainly stupid details, and things I think we should fix, but there is *not* the usual red flag of "Christ, somebody did something _really_ wrong". So I'm not in fact arguing against Minchan's patch of upping THREAD_SIZE_ORDER to 2 on x86-64, but at the same time stack size does remain one of my "we really need to be careful" issues, so while I am basically planning on applying that patch, I _also_ want to make sure that we fix the problems we do see and not just paper them over. The 8kB stack has been somewhat restrictive and painful for a while, and I'm ok with admitting that it is just getting _too_ damn painful, but I don't want to just give up entirely when we have a known deep stack case. Linus -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to firstname.lastname@example.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"email@example.com"> firstname.lastname@example.org </a>
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