From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: [PATCH/RFC 2/2] Mem Policy: Fixup Shm and Interleave Policy Reference Counting From: Lee Schermerhorn In-Reply-To: References: <20071010205837.7230.42818.sendpatchset@localhost> <20071010205849.7230.81877.sendpatchset@localhost> Content-Type: text/plain Date: Thu, 11 Oct 2007 09:41:00 -0400 Message-Id: <1192110060.5036.4.camel@localhost> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Christoph Lameter Cc: akpm@linux-foundation.org, ak@suse.de, gregkh@suse.de, linux-mm@kvack.org, mel@skynet.ie, eric.whitney@hp.com List-ID: On Wed, 2007-10-10 at 14:22 -0700, Christoph Lameter wrote: > On Wed, 10 Oct 2007, Lee Schermerhorn wrote: > > > * get_vma_policy() assumes that shared policies are referenced by > > the get_policy() vm_op, if any. This is true for shmem_get_policy() > > but not for shm_get_policy() when the "backing file" does not > > support a get_policy() vm_op. The latter is the case for SHM_HUGETLB > > segments. Because get_vma_policy() expects the get_policy() op to > > have added a ref, it doesn't do so itself. This results in > > premature freeing of the policy. Add the mpol_get() to the > > shm_get_policy() op when the backing file doesn't support shared > > policies. > > Could you add support for SHM_HUGETLB segments instead to make this > consistent so that shared policies always use a get_policy function? I have patches that do this as part of my shared policy series that is currently "on hold" while we sort these other things out. SHM_HUGETLB segments do use the shm_get_policy() vm_op. However, it detects that the hugetlb shm segment does not support get_policy(), so it just uses the vma policy at that address. You should like this behavior! :-). My patches implement shared policy for SHM_HUGETLB, which you don't like. So, I think we should leave this as is... for now. > > > * Further, shm_get_policy() was falling back to current task's task > > policy if the backing file did not support get_policy() vm_op and > > the vma policy was null. This is not valid when get_vma_policy() is > > called from show_numa_map() as task != current. Also, this did > > not match the behavior of the shmem_get_policy() vm_op which did > > NOT fall back to task policy. So, modify shm_get_policy() NOT to > > fall back to current->mempolicy. > > Hmmm..... The show_numa_map issue is special. Maybe fix that one instead? > > > Index: Linux/include/linux/mempolicy.h > > =================================================================== > > --- Linux.orig/include/linux/mempolicy.h 2007-10-10 13:36:44.000000000 -0400 > > +++ Linux/include/linux/mempolicy.h 2007-10-10 14:20:28.000000000 -0400 > > @@ -2,6 +2,7 @@ > > #define _LINUX_MEMPOLICY_H 1 > > > > #include > > +#include > > I think we tried to avoid a heavy include here. mm.h is huge and draws in > lots of other include files. The additional include is only needed for the > VM_BUG_ON it seems? BUG_ON would also work. Yeah, I know. However, I like the idea of having a separately configurable VM debug check. I will remove the include and the VM_BUG_ON for now. But, what would [any one else?] think about moving VM_BUG_ON() to asm-generic/bug.h in a separate patch? Lee -- 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