From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752665AbbKXHDd (ORCPT ); Tue, 24 Nov 2015 02:03:33 -0500 Received: from mail-pa0-f41.google.com ([209.85.220.41]:36684 "EHLO mail-pa0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752448AbbKXHDW (ORCPT ); Tue, 24 Nov 2015 02:03:22 -0500 Date: Tue, 24 Nov 2015 16:03:11 +0900 From: Minchan Kim To: Sergey Senozhatsky Cc: Andrew Morton , linux-kernel@vger.kernel.org, Kyeongdon Kim , Sergey Senozhatsky Subject: Re: [PATCH 2/3] zram: try vmalloc() after kmalloc() Message-ID: <20151124070311.GB7708@blaptop> References: <1448337696-10689-1-git-send-email-minchan@kernel.org> <20151124061258.GJ705@swordfish> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151124061258.GJ705@swordfish> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 24, 2015 at 03:12:58PM +0900, Sergey Senozhatsky wrote: > [..] > > static void *zcomp_lz4_create(void) > > { > > - return kzalloc(LZ4_MEM_COMPRESS, GFP_KERNEL); > > + void *ret; > > + > > + /* > > + * This function could be called in swapout/fs write path > > + * so we couldn't use GFP_FS|IO. And it assumes we already > > + * have at least one stream in zram initialization so we > > + * don't do best effort to allocate more stream in here. > > + * A default stream will work well without further multiple > > + * stream. That's why we use __GFP_NORETRY|NOWARN|NOMEMALLOC. > > + */ > > + ret = kzalloc(LZ4_MEM_COMPRESS, > > + __GFP_NORETRY|__GFP_NOWARN|__GFP_NOMEMALLOC); > > + if (!ret) > > + ret = __vmalloc(LZ4_MEM_COMPRESS, > > + __GFP_NORETRY|__GFP_NOWARN| > > + __GFP_NOMEMALLOC|__GFP_ZERO, > > + PAGE_KERNEL); > > + return ret; > > } > [..] > > so this change is still questionable. is there a real value in having > a vmalloc() fallback in the middle of allocations sequence: > > zstrm = kmalloc(sizeof(*zstrm), GFP_NOIO); > ^^^ ok, can fail here > > zstrm->zstrm->private = comp->backend->create(); > ^^^ kzalloc() and vmalloc() fallback ?? > > zstrm->buffer = (void *)__get_free_pages(GFP_NOIO | __GFP_ZERO, 1); > ^^^ can fail here again. > > can you please comment on this? Good question. Actually, failure of allocation came from backend->create as Kyeongdon's comment because it requires order-3 allocation which is very fragile in embedded system recenlty(Android, webOS. That's why Joonsoo are solving the trouble by fixing compaction part). Otherwise, other kmalloc/vmalloc stuff in our example would be almost no trouble in real practice(Of course, if you says it might, you're absolutely right. It could fail but I think it's *really* rare in real practice). More concern is order-1 allocation rather than kmalloc/vmalloc. I've got lots of allocation failure reports from product team until now and frankly speaking, I don't get such order-1 fail report until now. I guess the reason is that system is almost trobule due to heavy fragmentation before the notice such failure. So, I think if we solve order-3 allocation in backend->create, above problem will be almost solved. > > > and I'd prefer it to be a bit different -- use likely path first and > avoid an assignment in unlikely path. Personally, I like one return case unless other is really better for performance. I have trained it for Andrew, I belive. :) But if you don't like this by performance reason, I will add unlikely for vmalloc path. If you hate it just by personal preferenece, please I want to stick my code. > ... and add GFP_NOIO to both kzalloc() and __vmalloc(). I can add it. The harmness is really ignorable but as I mentioned at reply of Andrew, what's the benefit with GFP_NOIO? We couldn't make forward progress with __GFP_RECLAIM in reclaim context. > > and there is no __GFP_HIGHMEM in __vmalloc() call? Good to have. Thanks for the hint! Thanks. > > something like this: > > --- > > > ret = kzalloc(LZ4_MEM_COMPRESS, GFP_NOIO | __GFP_NORETRY | > __GFP_NOWARN | __GFP_NOMEMALLOC); > if (ret) > return ret; > > return __vmalloc(LZ4_MEM_COMPRESS, > GFP_NOIO | __GFP_NOWARN | __GFP_HIGHMEM | __GFP_ZERO, > PAGE_KERNEL); > > > -ss -- Kind regards, Minchan Kim