From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752633AbcAEPmR (ORCPT ); Tue, 5 Jan 2016 10:42:17 -0500 Received: from mail-io0-f179.google.com ([209.85.223.179]:33043 "EHLO mail-io0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752055AbcAEPmK (ORCPT ); Tue, 5 Jan 2016 10:42:10 -0500 Date: Tue, 5 Jan 2016 16:42:07 +0100 From: Michal Hocko To: Al Viro Cc: Geert Uytterhoeven , Linus Torvalds , Linux Kernel Mailing List , linux-mm@kvack.org Subject: Re: [RFC] free_pages stuff Message-ID: <20160105154207.GF15324@dhcp22.suse.cz> References: <20151221234615.GW20997@ZenIV.linux.org.uk> <20151222010403.GX20997@ZenIV.linux.org.uk> <20151222022226.GY20997@ZenIV.linux.org.uk> <20151222210435.GB20997@ZenIV.linux.org.uk> <20160105135903.GA15594@dhcp22.suse.cz> <20160105152602.GR9938@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160105152602.GR9938@ZenIV.linux.org.uk> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 05-01-16 15:26:02, Al Viro wrote: > On Tue, Jan 05, 2016 at 02:59:03PM +0100, Michal Hocko wrote: > > > > 3) vmalloc() is for large allocations. They will be page-aligned, > > > but *not* physically contiguous. OTOH, large physically contiguous > > > allocations are generally a bad idea. Unlike other allocators, there's > > > no variant that could be used in interrupt; freeing is possible there, > > > but allocation is not. Note that non-blocking variant *does* exist - > > > __vmalloc(size, GFP_ATOMIC, PAGE_KERNEL) can be used in atomic > > > contexts; it's the interrupt ones that are no-go. > > The last sentence I'd put into that part was complete crap... > > > It is also hardcoded GFP_KERNEL context so a usage from NOFS context > > needs a special treatment. > > ... in part because of this. GFP_ATOMIC __vmalloc() will be anything but, > and the only caller passing that is almost certainly bogus. Agreed as just replied in the other email thread which I have noticed only now. > As for NOFS/NOIO, > I wonder if we should apply that special treatment inside __vmalloc_area_node > rather than in callers; see the current thread on linux-mm for details... That would make a lot of sense to me. Spreading the _special_ treatment all over the kernel is certainly worse. > Another interesting issue is __GFP_HIGHMEM meaning for kmalloc and __vmalloc > resp. (should never be passed to kmalloc, should almost always be passed > to __vmalloc - the former needs pages mapped in kernel space, the latter > probably never needs a separate kernel alias for the data pages, to such > degree that I'm not sure if we shouldn't _force_ __GFP_HIGHMEM for data pages > allocation in __vmalloc_area_node()) I would have to think about this one some more. Let's not fragment the discussion and continue in that email thread: http://lkml.kernel.org/r/20160103071246.GK9938%40ZenIV.linux.org.uk -- Michal Hocko SUSE Labs