From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx103.postini.com [74.125.245.103]) by kanga.kvack.org (Postfix) with SMTP id 49EAC6B0002 for ; Mon, 28 Jan 2013 08:47:12 -0500 (EST) Message-ID: <51068155.4020807@redhat.com> Date: Mon, 28 Jan 2013 14:47:01 +0100 From: Jerome Marchand MIME-Version: 1.0 Subject: Re: [RESEND PATCH v5 1/4] zram: Fix deadlock bug in partial write References: <1359333506-13599-1-git-send-email-minchan@kernel.org> <51065FD4.6090200@redhat.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Pekka Enberg Cc: Minchan Kim , Greg Kroah-Hartman , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Dan Magenheimer , Nitin Gupta , Konrad Rzeszutek Wilk , Seth Jennings , stable@vger.kernel.org On 01/28/2013 02:26 PM, Pekka Enberg wrote: > On Mon, Jan 28, 2013 at 1:24 PM, Jerome Marchand wrote: >> On 01/28/2013 08:16 AM, Pekka Enberg wrote: >>> On Mon, Jan 28, 2013 at 2:38 AM, Minchan Kim wrote: >>>> Now zram allocates new page with GFP_KERNEL in zram I/O path >>>> if IO is partial. Unfortunately, It may cuase deadlock with >>> >>> s/cuase/cause/g >>> >>>> reclaim path so this patch solves the problem. >>> >>> It'd be nice to know about the problem in more detail. I'm also >>> curious on why you decided on GFP_ATOMIC for the read path and >>> GFP_NOIO in the write path. >> >> This is because we're holding a kmap_atomic page in the read path. > > Okay, so that's about partial *reads* and not even mentioned in the > changelog, no? > > AFAICT, you could rearrange the code in zram_bvec_read() as follows: > > if (is_partial_io(bvec)) > /* Use a temporary buffer to decompress the page */ > uncmem = kmalloc(PAGE_SIZE, GFP_KERNEL); > else { > uncmem = user_mem = kmap_atomic(page); > } > > and avoid the GFP_ATOMIC allocation. > user_mem still has to be mapped in case of partial I/O too. But the temporary buffer allocation could happen before. The allocation still would need to be GFP_NOIO to avoid possible deadlocks. Anyhow, the commit message could definitely be more explicit. Regards, Jerome -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org