From mboxrd@z Thu Jan 1 00:00:00 1970 From: Theodore Ts'o Subject: Re: [PATCH 2/3] f2fs crypto: use bounce pages from mempool first Date: Mon, 25 May 2015 15:55:51 -0400 Message-ID: <20150525195551.GB16402@thunk.org> References: <1432255225-76792-1-git-send-email-jaegeuk@kernel.org> <1432255225-76792-2-git-send-email-jaegeuk@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net To: Jaegeuk Kim Return-path: Content-Disposition: inline In-Reply-To: <1432255225-76792-2-git-send-email-jaegeuk@kernel.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linux-f2fs-devel-bounces@lists.sourceforge.net List-Id: linux-fsdevel.vger.kernel.org On Thu, May 21, 2015 at 05:40:24PM -0700, Jaegeuk Kim wrote: > If a lot of write streams are triggered, alloc_page and __free_page are > costly called, resulting in high memory pressure. > > In order to avoid that, let's reuse mempool pages for writeback pages. The reason why the mempool pages was used as a fallback was because once we are deep in the writeback code, handling memory allocation failures is close to impossible, since we've already made enough changes that unwinding them would be extremely difficult. So the basic idea was to use the mempool as an emergency reserve, since Failure Is Not An Option, and the alternative, which is to simply loop until the mm subsystem sees fit to give us a page, has sometimes led to deadlock. The primary source of write streams should be either (a) fsync operations, or (b) calls from the writeback thread. Are there any additional sources for f2fs? If they are calls from fsync operations, and we have more than a threshold number of write operations in play, we might want to think about blocking the fsync/fdatasync writeback, **before** the operation starts taking locks, so other write operations can proceed. And the writeback thread should keep the number of write operations to a reasonable number, especially given that we are treating page encryption as a blocking operation. Or is there something else going on which is making this to be more of a problem for f2fs? Regards, - Ted ------------------------------------------------------------------------------ One dashboard for servers and applications across Physical-Virtual-Cloud Widest out-of-the-box monitoring support with 50+ applications Performance metrics, stats and reports that give you Actionable Insights Deep dive visibility with transaction tracing using APM Insight. http://ad.doubleclick.net/ddm/clk/290420510;117567292;y