From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt0-f198.google.com (mail-qt0-f198.google.com [209.85.216.198]) by kanga.kvack.org (Postfix) with ESMTP id 6EF676B0006 for ; Tue, 17 Apr 2018 15:09:11 -0400 (EDT) Received: by mail-qt0-f198.google.com with SMTP id d5so12989935qtg.7 for ; Tue, 17 Apr 2018 12:09:11 -0700 (PDT) Received: from mx1.redhat.com (mx3-rdu2.redhat.com. [66.187.233.73]) by mx.google.com with ESMTPS id i28si6251302qta.77.2018.04.17.12.09.10 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 17 Apr 2018 12:09:10 -0700 (PDT) Date: Tue, 17 Apr 2018 15:09:09 -0400 (EDT) From: Mikulas Patocka Subject: Re: [PATCH RESEND] slab: introduce the flag SLAB_MINIMIZE_WASTE In-Reply-To: Message-ID: References: <20c58a03-90a8-7e75-5fc7-856facfb6c8a@suse.cz> <20180413151019.GA5660@redhat.com> <20180416142703.GA22422@redhat.com> <20180416144638.GA22484@redhat.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Christopher Lameter Cc: Vlastimil Babka , Mike Snitzer , Matthew Wilcox , Pekka Enberg , linux-mm@kvack.org, dm-devel@redhat.com, David Rientjes , Joonsoo Kim , Andrew Morton , linux-kernel@vger.kernel.org On Tue, 17 Apr 2018, Christopher Lameter wrote: > On Tue, 17 Apr 2018, Vlastimil Babka wrote: > > > On 04/17/2018 04:45 PM, Christopher Lameter wrote: > > > > But then higher order allocs are generally seen as problematic. > > > > I think in this case they are better than wasting/fragmenting 384kB for > > 640kB object. > > Well typically we have suggested that people use vmalloc in the past. vmalloc is slow - it is unuseable for a buffer cache. > > > That > > > means that callers need to be able to tolerate failures. > > > > Is it any different from now? I suppose there would still be > > smallest-order fallback involved in sl*b itself? And if your allocation > > is so large it can fail even with the fallback (i.e. >= costly order), > > you need to tolerate failures anyway? > > Failures can occur even with < costly order as far as I can telkl. Order 0 > is the only safe one. The alloc_pages functions seems to retry indefinitely for order <= PAGE_ALLOC_COSTLY_ORDER. Do you have some explanation why it should fail? > > One corner case I see is if there is anyone who would rather use their > > own fallback instead of the space-wasting smallest-order fallback. > > Maybe we could map some GFP flag to indicate that. > > Well if you have a fallback then maybe the slab allocator should not fall > back on its own but let the caller deal with it. Mikulas