From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <4612C401.3010507@redhat.com> Date: Tue, 03 Apr 2007 17:15:45 -0400 From: Rik van Riel MIME-Version: 1.0 Subject: Re: missing madvise functionality References: <46128051.9000609@redhat.com> <46128CC2.9090809@redhat.com> <20070403172841.GB23689@one.firstfloor.org> <20070403125903.3e8577f4.akpm@linux-foundation.org> <4612B645.7030902@redhat.com> <20070403135154.61e1b5f3.akpm@linux-foundation.org> <4612C059.8070702@redhat.com> <4612C2B6.3010302@cosmosbay.com> In-Reply-To: <4612C2B6.3010302@cosmosbay.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org Return-Path: To: Eric Dumazet Cc: Andrew Morton , Ulrich Drepper , Andi Kleen , Linux Kernel , Jakub Jelinek , linux-mm@kvack.org, Hugh Dickins List-ID: Eric Dumazet wrote: > Rik van Riel a A(C)crit : >> Andrew Morton wrote: >> >>> Oh. I was assuming that we'd want to unmap these pages from >>> pagetables and >>> mark then super-easily-reclaimable. So a later touch would incur a >>> minor >>> fault. >>> >>> But you think that we should leave them mapped into pagetables so no >>> such >>> fault occurs. >> >>> Leaving the pages mapped into pagetables means that they are >>> considerably >>> less likely to be reclaimed. >> >> If we move the pages to a place where they are very likely to be >> reclaimed quickly (end of the inactive list, or a separate >> reclaim list) and clear the dirty and referenced lists, we can >> both reclaim the page easily *and* avoid the page fault penalty. >> > > There is one possible speedup : > > - If an user app does a madvise(MADV_DONTNEED), we can assume the pages > can later be bring back without need to zero them. The application > doesnt care. ... however, the application that previously used that page might care a lot! > mmap()/brk() must give fresh NULL pages, but maybe > madvise(MADV_DONTNEED) can relax this requirement (if the pages were > reclaimed, then a page fault could bring a new page with random content) If we bring in a new page, it has to be zeroed for security reasons. You don't want somebody else's process to get a page with your password in it. -- 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