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a="165207688" X-IronPort-AV: E=Sophos;i="5.77,372,1596524400"; d="scan'208";a="165207688" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 13 Oct 2020 15:44:00 -0700 IronPort-SDR: 5+3pqF9CmBPt+wvceaHBdji8VYQunquEWnY3sHNAKPiKcA0IEW2aS21IIQNt2KuXcgOCDsn35U yD+n4jKBfDnQ== X-IronPort-AV: E=Sophos;i="5.77,372,1596524400"; d="scan'208";a="346335779" Received: from murawskx-mobl.amr.corp.intel.com (HELO [10.209.9.29]) ([10.209.9.29]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 13 Oct 2020 15:43:59 -0700 Subject: Re: [RFC PATCH 13/22] x86/fpu/xstate: Expand dynamic user state area on first use To: "Brown, Len" , Andy Lutomirski , "Bae, Chang Seok" Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , X86 ML , "Liu, Jing2" , "Shankar, Ravi V" , LKML References: <20201001203913.9125-1-chang.seok.bae@intel.com> <20201001203913.9125-14-chang.seok.bae@intel.com> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/13/20 3:31 PM, Brown, Len wrote: > vmalloc() does not fail, and does not return an error, and so there is no concept > of returning a signal. Well, the order-0 allocations are no-fail, as are the vmalloc kernel structures and the page tables that might have to be allocated. But, that's not guaranteed to be in place *forever*. I think we still need to check for and handle allocation failures, even if they're not known to be possible today. > If we got to the point where vmalloc() sleeps, then the system > has bigger OOM issues, and the OOM killer would be on the prowl. vmalloc() can *certainly* sleep. Allocation failures mean returning NULL from the allocator, and the very way we avoid doing that is by sleeping to go reclaim some memory from some other allocation. Sleeping is a normal and healthy part of handling allocation requests, including vmalloc(). > If we were concerned about using vmalloc for a couple of pages in the task structure, > Then we could implement a routine to harvest unused buffers and free them -- > but that didn't seem worth the complexity. Note that this feature is 64-bit only. IMNHO, vmalloc() is overkill for ~10k, which is roughly the size of the XSAVE buffer for the first AMX implementation. But, it's not overkill for the ~66k of space that will be needed if some CPU implementation comes along and uses all of the architectural space AMX provides.