From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752230AbcAEP0L (ORCPT ); Tue, 5 Jan 2016 10:26:11 -0500 Received: from zeniv.linux.org.uk ([195.92.253.2]:57930 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751623AbcAEP0H (ORCPT ); Tue, 5 Jan 2016 10:26:07 -0500 Date: Tue, 5 Jan 2016 15:26:02 +0000 From: Al Viro To: Michal Hocko Cc: Geert Uytterhoeven , Linus Torvalds , Linux Kernel Mailing List , linux-mm@kvack.org Subject: Re: [RFC] free_pages stuff Message-ID: <20160105152602.GR9938@ZenIV.linux.org.uk> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160105135903.GA15594@dhcp22.suse.cz> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. 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... 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()) > > 4) if it's very early in bootstrap, alloc_bootmem() and friends > > may be the only option. Rule of the thumb: if it's already printed > > Memory: ...../..... available..... > > you shouldn't be using that one. Allocations are physically contiguous > > and at that point large physically contiguous allocations are still OK. Probably needs at least some discussion of memblock vs. bootmem APIs.