From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: Re: [PATCH] mm: create a separate slab for page->ptl allocation Date: Tue, 5 Nov 2013 15:56:19 -0800 Message-ID: <20131105155619.021f32eba1ca8f15a73ed4c9@linux-foundation.org> References: <1382442839-7458-1-git-send-email-kirill.shutemov@linux.intel.com> <20131105150145.734a5dd5b5d455800ebfa0d3@linux-foundation.org> <20131105224217.GC20167@shutemov.name> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20131105224217.GC20167@shutemov.name> Sender: owner-linux-mm@kvack.org To: "Kirill A. Shutemov" Cc: "Kirill A. Shutemov" , Peter Zijlstra , Ingo Molnar , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org List-Id: linux-arch.vger.kernel.org On Wed, 6 Nov 2013 00:42:17 +0200 "Kirill A. Shutemov" wrote: > > > #if USE_SPLIT_PTE_PTLOCKS > > > +struct kmem_cache *page_ptl_cachep; > > > +void __init ptlock_cache_init(void) > > > +{ > > > + if (sizeof(spinlock_t) > sizeof(long)) > > > + page_ptl_cachep = kmem_cache_create("page->ptl", > > > + sizeof(spinlock_t), 0, SLAB_PANIC, NULL); > > > +} > > > > Confused. If (sizeof(spinlock_t) > sizeof(long)) happens to be false > > then the kernel will later crash. It would be better to use BUILD_BUG_ON() > > here, if that works. Otherwise BUG_ON. > > if (sizeof(spinlock_t) > sizeof(long)) is false, we don't need dynamicly > allocate page->ptl. It's embedded to struct page itself. __ptlock_alloc() > never called in this case. OK. Please add a comment explaining this so the next reader doesn't get tripped up like I was. Really the function shouldn't exist in this case. It is __init so the sin is not terrible, but can this be arranged? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:59523 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755916Ab3KEX4U (ORCPT ); Tue, 5 Nov 2013 18:56:20 -0500 Date: Tue, 5 Nov 2013 15:56:19 -0800 From: Andrew Morton Subject: Re: [PATCH] mm: create a separate slab for page->ptl allocation Message-ID: <20131105155619.021f32eba1ca8f15a73ed4c9@linux-foundation.org> In-Reply-To: <20131105224217.GC20167@shutemov.name> References: <1382442839-7458-1-git-send-email-kirill.shutemov@linux.intel.com> <20131105150145.734a5dd5b5d455800ebfa0d3@linux-foundation.org> <20131105224217.GC20167@shutemov.name> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: "Kirill A. Shutemov" Cc: "Kirill A. Shutemov" , Peter Zijlstra , Ingo Molnar , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org Message-ID: <20131105235619.PqreyiLz1HacP_Mq3vRv141CNESJDzmrI6Hi31dXVb4@z> On Wed, 6 Nov 2013 00:42:17 +0200 "Kirill A. Shutemov" wrote: > > > #if USE_SPLIT_PTE_PTLOCKS > > > +struct kmem_cache *page_ptl_cachep; > > > +void __init ptlock_cache_init(void) > > > +{ > > > + if (sizeof(spinlock_t) > sizeof(long)) > > > + page_ptl_cachep = kmem_cache_create("page->ptl", > > > + sizeof(spinlock_t), 0, SLAB_PANIC, NULL); > > > +} > > > > Confused. If (sizeof(spinlock_t) > sizeof(long)) happens to be false > > then the kernel will later crash. It would be better to use BUILD_BUG_ON() > > here, if that works. Otherwise BUG_ON. > > if (sizeof(spinlock_t) > sizeof(long)) is false, we don't need dynamicly > allocate page->ptl. It's embedded to struct page itself. __ptlock_alloc() > never called in this case. OK. Please add a comment explaining this so the next reader doesn't get tripped up like I was. Really the function shouldn't exist in this case. It is __init so the sin is not terrible, but can this be arranged?