From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: [v4][PATCH 2/2] fix large pages in pagemap From: Matt Mackall In-Reply-To: <1213219435.20475.44.camel@nimitz> References: <20080611180228.12987026@kernel> <20080611180230.7459973B@kernel> <20080611123724.3a79ea61.akpm@linux-foundation.org> <1213213980.20045.116.camel@calx> <20080611131108.61389481.akpm@linux-foundation.org> <1213216462.20475.36.camel@nimitz> <20080611135207.32a46267.akpm@linux-foundation.org> <1213219435.20475.44.camel@nimitz> Content-Type: text/plain Date: Wed, 11 Jun 2008 17:37:05 -0500 Message-Id: <1213223825.20045.138.camel@calx> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Dave Hansen Cc: Andrew Morton , hans.rosenfeld@amd.com, linux-mm@kvack.org, hugh@veritas.com, riel@redhat.com, nacc , Adam Litke List-ID: On Wed, 2008-06-11 at 14:23 -0700, Dave Hansen wrote: > On Wed, 2008-06-11 at 13:52 -0700, Andrew Morton wrote: > > access_process_vm-device-memory-infrastructure.patch is a powerpc > > feature, and it uses pmd_huge(). > > I think that's bogus. It probably needs to check the VMA in > generic_access_phys() if it wants to be safe. I don't see any way that > pmd_huge() can give anything back other than 0 on ppc: > > arch/powerpc/mm/hugetlbpage.c: > > int pmd_huge(pmd_t pmd) > { > return 0; > } > > or in include/linux/hugetlb.h: > > #define pmd_huge(x) 0 > > > Am I missing something, or is pmd_huge() a whopping big grenade for x86 > > developers to toss at non-x86 architectures? It seems quite dangerous. > > Yeah, it isn't really usable outside of arch code, although it kinda > looks like it. That begs the question: if we can't use it reliably outside of arch code, why do other arches even bother defining it? And the answer seems to be because of the two uses in mm/memory.c. The first seems like it could be avoided with an implementation of follow_huge_addr on x86. The second is either bogus (only works on x86) or superfluous (not needed at all), no? -- Mathematics is the supreme nostalgia of our time. -- 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