From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <38022640.3447ECA6@colorfullife.com> Date: Mon, 11 Oct 1999 20:02:40 +0200 From: Manfred Spraul MIME-Version: 1.0 Subject: Re: locking question: do_mmap(), do_munmap() References: Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Alexander Viro Cc: "Stephen C. Tweedie" , Andrea Arcangeli , linux-kernel@vger.rutgers.edu, Ingo Molnar , linux-mm@kvack.org List-ID: Alexander Viro wrote: > > On Mon, 11 Oct 1999, Stephen C. Tweedie wrote: > > > Hi, > > > > On Sun, 10 Oct 1999 15:03:45 -0400 (EDT), Alexander Viro > > said: > > > > > Hold on. In swap_out_mm() you have to protect find_vma() (OK, it doesn't > > > block, but we'll have to take care of mm->mmap_cache) _and_ you'll have to > > > protect vma from destruction all way down to try_to_swap_out(). And to > > > vma->swapout(). Which can sleep, so spinlocks are out of question > > > here. > > > > No, spinlocks would be ideal. The vma swapout codes _have_ to be > > prepared for the vma to be destroyed as soon as we sleep. In fact, the > > entire mm may disappear if the process happens to exit. Once we know > > which page to write where, the swapout operation becomes a per-page > > operation, not per-vma. > > Aha, so you propose to drop it in ->swapout(), right? (after get_file() in > filemap_write_page()... Ouch. Probably we'ld better lambda-expand the call > in filemap_swapout() - the thing is called from other places too)... What about something like a rw-semaphore which protects the vma list: vma-list modifiers [ie merge_segments(), insert_vm_struct() and do_munmap()] grab it exclusive, swapper grabs it "shared, starve exclusive". All other vma-list readers are protected by mm->mmap_sem. This should not dead-lock, and no changes are required in vm_ops->swapout(). -- Manfred -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://humbolt.geo.uu.nl/Linux-MM/