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Tue, 18 Aug 2020 12:22:16 -0400 X-MC-Unique: v2ZKtLzmPAWzf0xDvdMpzQ-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id D6BF31014DFB; Tue, 18 Aug 2020 16:22:13 +0000 (UTC) Received: from [10.36.113.168] (ovpn-113-168.ams2.redhat.com [10.36.113.168]) by smtp.corp.redhat.com (Postfix) with ESMTP id F2FF76CE4E; Tue, 18 Aug 2020 16:22:10 +0000 (UTC) Subject: Re: [RFC 0/7] Support high-order page bulk allocation To: Matthew Wilcox , Minchan Kim Cc: Andrew Morton , linux-mm , Joonsoo Kim , Vlastimil Babka , John Dias , Suren Baghdasaryan , pullip.cho@samsung.com, Chris Goldsworthy , Nicholas Piggin References: <20200814173131.2803002-1-minchan@kernel.org> <4e2bd095-b693-9fed-40e0-ab538ec09aaa@redhat.com> <20200817152706.GB3852332@google.com> <20200817163018.GC3852332@google.com> <20200817233442.GD3852332@google.com> <7c07e8cf-6adc-92be-d819-d60a389559d8@redhat.com> <20200818151543.GE3852332@google.com> <20200818155825.GS17456@casper.infradead.org> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20200818155825.GS17456@casper.infradead.org> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=david@redhat.com X-Mimecast-Spam-Score: 0.003 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 X-Rspamd-Queue-Id: 452216C1D X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 18.08.20 17:58, Matthew Wilcox wrote: > On Tue, Aug 18, 2020 at 08:15:43AM -0700, Minchan Kim wrote: >> I understand pfn stuff in the API is not pretty but the concept of ide= a >> makes sense to me in that go though the *migratable area* and get poss= ible >> order pages with hard effort. It looks like GFP_NORETRY version for >> kmem_cache_alloc_bulk. >> >> How about this? >> >> int cma_alloc(struct cma *cma, int order, unsigned int nr_elem, st= ruct page **pages); >=20 > I think that makes a lot more sense as an API. Although I think you wa= nt >=20 > int cma_bulk_alloc(struct cma *cma, unsigned order, unsigned nr_elem, > struct page **pages); >=20 Right, and I would start with a very simple implementation that does not mess with alloc_contig_range() (meaning: modify it). I'd then much rather want to see simple tweaks to alloc_contig_range() to improve the situation. E.g., some kind of "fail fast" flag that let's the caller specify to skip some draining (or do it manually in cma before a bulk allocation) and rather fail fast than really trying to allocate the range whatever it costs. There are multiple optimizations you can play with then (start with big granularity and split, move to smaller granularity on demand, etc., all nicely wrapped in cma_bulk_alloc()). Yes, it might not end up as fast as this big hack (sorry) here, but as Nicholas correctly said, it's not our motivation to implement and maintain such complexity just to squeeze the last milliseconds out of an allocation path for "broken devices". I absolutely dislike pushing this very specific allocation policy down to the core range allocator. It's already makes my head spin every time I look at it in detail. --=20 Thanks, David / dhildenb