From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from dax.scot.redhat.com (sct@dax.scot.redhat.com [195.89.149.242]) by kvack.org (8.8.7/8.8.7) with ESMTP id JAA16492 for ; Tue, 19 Jan 1999 09:32:54 -0500 Date: Tue, 19 Jan 1999 14:32:34 GMT Message-Id: <199901191432.OAA05326@dax.scot.redhat.com> From: "Stephen C. Tweedie" MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Subject: Re: Why don't shared anonymous mappings work? In-Reply-To: <199901132131.OAA09149@nyx10.nyx.net> References: <199901132131.OAA09149@nyx10.nyx.net> Sender: owner-linux-mm@kvack.org To: Colin Plumb Cc: sct@redhat.com, linux-mm@kvack.orgStephen Tweedie List-ID: Hi, On Wed, 13 Jan 1999 14:31:41 -0700 (MST), Colin Plumb said: > Um, I just thought of another problem with shared anonymous pages. > It's similar to the zero-page issue you raised, but it's no longer > a single special case. > Copy-on-write and shared mappings. Let's say that process 1 has a COW > copy of page X. Then the page is shared (via mmap /proc/1/mem or some > such) with process 2. Now process A writes to the page. Invalid argument. This is *precisely* why mmap of /proc/X/mem is broken. We don't need to implement reasonable semantics for that case, because there _are_ no reasonable semantics for a page which can be both MAP_PRIVATE and MAP_SHARED in the same process. --Stephen -- This is a majordomo managed list. To unsubscribe, send a message with the body 'unsubscribe linux-mm me@address' to: majordomo@kvack.org