From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Masover Subject: Re: [PATCH] reiserfs: eliminate minimum window size for bitmap searching Date: Tue, 22 Aug 2006 10:33:45 -0500 Message-ID: <44EB23D9.9000508@slaphack.com> References: <44EB1484.2040502@suse.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <44EB1484.2040502@suse.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: Jeff Mahoney Cc: Andrew Morton , Linus Torvalds , Linux Kernel Mailing List , ReiserFS List , Mike Benoit Jeff Mahoney wrote: > When a file system becomes fragmented (using MythTV, for example), the > bigalloc window searching ends up causing huge performance problems. In > a file system presented by a user experiencing this bug, the file system > was 90% free, but no 32-block free windows existed on the entire file system. > This causes the allocator to scan the entire file system for each 128k write > before backing down to searching for individual blocks. Question: Would it be better to take that performance hit once, then cache the result for awhile? If we can't find enough consecutive space, such space isn't likely to appear until a lot of space is freed or a repacker is run. > In the end, finding a contiguous window for all the blocks in a write is > an advantageous special case, but one that can be found naturally when > such a window exists anyway. Hmm. Ok, I don't understand how this works, so I'll shut up.