Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1765396AbXFGPvW (ORCPT ); Thu, 7 Jun 2007 11:51:22 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752341AbXFGPvP (ORCPT ); Thu, 7 Jun 2007 11:51:15 -0400 Received: from x35.xmailserver.org ([64.71.152.41]:1093 "EHLO x35.xmailserver.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755516AbXFGPvO (ORCPT ); Thu, 7 Jun 2007 11:51:14 -0400 X-AuthUser: davidel@xmailserver.org Date: Thu, 7 Jun 2007 08:51:11 -0700 (PDT) From: Davide Libenzi X-X-Sender: davide@alien.or.mcafeemobile.com To: Eric Dumazet cc: Kyle Moffett , Alan Cox , Ulrich Drepper , Linux Kernel Mailing List , Linus Torvalds , Andrew Morton , Ingo Molnar Subject: Re: [patch 7/8] fdmap v2 - implement sys_socket2 In-Reply-To: <20070607151243.22caab9e.dada1@cosmosbay.com> Message-ID: References: <20070606235906.72439d16@the-village.bc.nu> <20070607001932.35c9591c@the-village.bc.nu> <466741BD.20106@redhat.com> <20070607110432.73be7960@the-village.bc.nu> <20070607151243.22caab9e.dada1@cosmosbay.com> X-GPG-FINGRPRINT: CFAE 5BEE FD36 F65E E640 56FE 0974 BF23 270F 474E X-GPG-PUBLIC_KEY: http://www.xmailserver.org/davidel.asc MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2076 Lines: 56 On Thu, 7 Jun 2007, Eric Dumazet wrote: > On Thu, 7 Jun 2007 07:59:47 -0400 > Kyle Moffett wrote: > > > > Likewise there are a massive group of other libraries (especially > > user-interface and server related ones) that would really like to > > have support for creating file-descriptors without the top-level > > application closing them randomly (like several shells seem to). > > > > True, shells are sometimes quite strange. > > For example, bash uses file descriptor 255 (FD_CLOEXEC) > > When it forks a new process, child gets a file table with 256 slots. > > At exec() time, 255 is closed but file table doesnt shrink. > (shrinking is done at fork() time only) > > With fdmap, that means each process started by bash uses at least > 256 * sizeof(list_head) bytes, ie 4096 bytes on x86_64, even if only three > file-descriptors are opened (0,1,2) > > FD_CLOFORK should help here (BTW : current patch from Davide doesnt take this > into account and might need a change in fdmap_top_open_fd()) Yes, the CLOFORK flag is there, but it needs to be taken in account in fdmap_top_open_fd(). > Davide, are you sure we want FIFO for non sequential allocations ? > > This tends to use all the fmap slots, and not very cache friendly > if an app does a lot of [open(),...,close()] things. We already got a > perf drop because of RCUification of file freeing (FIFO mode instead > of LIFO given by kmalloc()/kfree()) > > If the idea behind this FIFO was security (ie not easy for an app to predict > next glibc file handle), we/glibc might use yet another FD_SECUREMODE flag, > wich ORed with O_NONSEQFD would ask to fdmap_newfd() to take the tail of > fmap->slist, not head. That was the reason, yes. If we agree that the base randomization is enough, we can use a LIFO. - Davide - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/