From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with ESMTP id 72DDD6B0023 for ; Tue, 3 May 2011 16:11:04 -0400 (EDT) Received: by iwg8 with SMTP id 8so561640iwg.14 for ; Tue, 03 May 2011 13:11:02 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <201105032202.42662.arnd@arndb.de> References: <201105031516.28907.arnd@arndb.de> <201105032202.42662.arnd@arndb.de> Date: Tue, 3 May 2011 22:11:02 +0200 Message-ID: Subject: Re: mmc blkqueue is empty even if there are pending reads in do_generic_file_read() From: Per Forlin Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: Arnd Bergmann Cc: linux-mm@kvack.org, linux-mmc@vger.kernel.org, linaro-kernel@lists.linaro.org On 3 May 2011 22:02, Arnd Bergmann wrote: > On Tuesday 03 May 2011 20:54:43 Per Forlin wrote: >> >> page_not_up_to_date: >> >> /* Get exclusive access to the page ... */ >> >> error =3D lock_page_killable(page); >> > I looked at the code in do_generic_file_read(). lock_page_killable >> > waits until the current read ahead is completed. >> > Is it possible to configure the read ahead to push multiple read >> > request to the block device queue?add > > I believe sleeping in __lock_page_killable is the best possible scenario. > Most cards I've seen work best when you use at least 64KB reads, so it wi= ll > be faster to wait there than to read smaller units. > >> When I first looked at this I used dd if=3D/dev/mmcblk0 of=3D/dev/null b= s=3D1M count=3D4 >> If bs is larger than read ahead, this will make the execution loop in >> do_generic_file_read() reading 512 until 1M is read. The second time >> in this loop it will wait on lock_page_killable. >> >> If bs=3D16k the execution wont stuck at lock_page_killable. > > submitting small 512 byte read requests is a real problem when the > underlying page size is 16 KB. If your interpretation is right, > we should probably find a way to make it read larger chunks > on flash media. Sorry a typo. I missed out a "k" :) It reads 512k until 1M. > > =A0 =A0 =A0 =A0Arnd > Per -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org