From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <462C8B0A.8060801@redhat.com> Date: Mon, 23 Apr 2007 06:31:38 -0400 From: Rik van Riel MIME-Version: 1.0 Subject: Re: [PATCH] lazy freeing of memory through MADV_FREE References: <46247427.6000902@redhat.com> <20070420135715.f6e8e091.akpm@linux-foundation.org> <462932BE.4020005@redhat.com> <20070420150618.179d31a4.akpm@linux-foundation.org> <4629524C.5040302@redhat.com> <462ACA40.8070407@yahoo.com.au> <462B0156.9020407@redhat.com> <462BFAF3.4040509@yahoo.com.au> <462C2DC7.5070709@redhat.com> <462C2F33.8090508@redhat.com> <462C7A6F.9030905@redhat.com> <462C88B1.8080906@yahoo.com.au> In-Reply-To: <462C88B1.8080906@yahoo.com.au> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Nick Piggin Cc: Andrew Morton , linux-kernel , linux-mm , shak , jakub@redhat.com, drepper@redhat.com List-ID: Nick Piggin wrote: >> It looks like the tlb flushes (and IPIs) from zap_pte_range() >> could have been the problem. They're gone now. > > I guess it is a good idea to batch these things. But can you > do that on all architectures? What happens if your tlb flush > happens after another thread already accesses it again, or > after it subsequently gets removed from the address space via > another CPU? I have thought about this a lot tonight, and have come to the conclusion that they are ok. The reason is simple: 1) we do the TLB flush before we return from the madvise(MADV_FREE) syscall. 2) anything that accessess the pages between the start and end of the MADV_FREE procedure does not know in which order we go through the pages, so it could hit a page either before or after we get to processing it 3) because of this, we can treat any such accesses as happening simultaneously with the MADV_FREE and as illegal, aka undefined behaviour territory and we do not need to worry about them 4) because we flush the tlb before releasing the page table lock, other CPUs cannot remove this page from the address space - they will block on the page table lock before looking at this pte -- Politics is the struggle between those who want to make their country the best in the world, and those who believe it already is. Each group calls the other unpatriotic. -- 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