From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Moyer Subject: Re: [patch|rfc] block: don't mark buffers beyond end of disk as mapped Date: Tue, 01 May 2012 16:37:10 -0400 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, jaxboe@fusionio.com, Kyle McMartin To: Nick Piggin Return-path: Received: from mx1.redhat.com ([209.132.183.28]:28193 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751007Ab2EAUhO (ORCPT ); Tue, 1 May 2012 16:37:14 -0400 In-Reply-To: (Nick Piggin's message of "Wed, 2 May 2012 00:26:55 +1000") Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Nick Piggin writes: > On 2 May 2012 00:08, Jeff Moyer wrote: >> Nick Piggin writes: >> >>> Not a bad fix. But it's kind of sad to have i_size checking logic also in >>> block_read_full_page, that does not cope with this. >>> >>> I have found there are parts of the kernel (readahead) that try to read >>> beyond EOF and seem to get angry if we return an error (by not >>> marking uptodate in readpage) in that case though :( >>> >>> But, either way, I think it's very reasonable to not mark buffers beyond >>> end of device as mapped. So I think your patch is fine. >>> >>> I guess for ext[234], it does not read metadata close to the end of the >>> device or you were using 4K sized blocks? >> >> Well, the test case just reads directly from the loop device, bypassing >> the file system, and I did use 1KB blocks when making the file system, so >> it is quite puzzling. > > It's because buffer_head creation does not go through the same paths > for bdev file access versus getblk APIs. > > blkdev_get_block does the right thing there > > In fact, it's probably good to unify the checks here, i.e., use max_blocks() You really think it's worth it? I mean, it's just an i_size_read and a shift, and there is precedent for it inside fs/buffer.c. I'd prefer to keep the patch as-is, but will change it if you feel that strongly about it. Cheers, Jeff