From mboxrd@z Thu Jan 1 00:00:00 1970 From: Phillip Susi Subject: readahead man page incorrectly says it blocks Date: Thu, 02 Jan 2014 15:46:28 -0500 Message-ID: <52C5D024.1020906@ubuntu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit To: linux-mm@kvack.org, linux-fsdevel Return-path: Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 The man page for readahead(2) incorrectly claims that it blocks until all of the requested data has been read. I filed a bug last year to have this corrected, but I think it is being ignored now because they don't believe me that it isn't supposed to block. Could someone help back me up and get this fixed? https://bugzilla.kernel.org/show_bug.cgi?id=54271 -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.17 (MingW32) Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQEcBAEBAgAGBQJSxdAkAAoJEI5FoCIzSKrwA8MH/jNRBxTENfpaiB2qNpaxhv5i FGj4mJ/VEhgntg6iCK7KN1r796GpnG+PI0yAEHcXHsHB2o9JoyB1jnaTUEte3PAb anetZenfKHbq9pO5/5tYCLY8KX4pBp9xSI3G0SyeZ5aY5/jObj24jEswwViuYlvs 3Ma+zQxpcYnVht29NPhioUOmxBocJkvFleAemHrPydYb9Q6wuHYiIke61sjFYXYy 8sPHhuXfIb6W4NweHmI9RGhijfiRK8AjgUaGvmVx2CzQ5B0vfw0SmAfeMYodkwU5 7M+yyNCKn19IJSbALJ8E1BupHnhe2r3InRXLNfrWXy0JvkbgWFk+fAatkzIUpdQ= =tZiw -----END PGP SIGNATURE----- -- 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 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx180.postini.com [74.125.245.180]) by kanga.kvack.org (Postfix) with SMTP id AB9F86B0033 for ; Fri, 17 May 2013 10:54:24 -0400 (EDT) Message-ID: <5196449F.9080108@ubuntu.com> Date: Fri, 17 May 2013 10:54:23 -0400 From: Phillip Susi MIME-Version: 1.0 Subject: readahead man page incorrectly says it blocks Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: linux-mm@kvack.org -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 The man page for readahead(2) incorrectly claims that it blocks until all of the requested data has been read. I filed a bug a few months ago to have this corrected, but I think it is being ignored now because they don't believe me that it isn't supposed to block. Could someone help back me up and get this fixed? https://bugzilla.kernel.org/show_bug.cgi?id=54271 -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.17 (MingW32) Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQEcBAEBAgAGBQJRlkSfAAoJEJrBOlT6nu75vcIH/0bVb3BGAr+obffnDgugX+EB LAQaj/p83vNV9ND8alsSg0c+Q8iX8m4klSgsiYg78NdM8x0+V1je5n934/KqUTO1 eHWLf+7GcRJ7CuBctaY2U0uSWWrhMjhPqD1HBlTplqH3Wj3xxIf9T4Ym2K4+BW1Z yx2XAPhmWy57EBE4MtxUSVd01jINZZpyuv2oOCqblLfmUKTWzJvm12eDjnrYQq1/ Ar7trfjFE4HXIyTHIEgQazoi9D4dF8yFHgndd89ZQ2yvSkwe59UXDyequm6IrOCz mAqIwUS0N5xJ1AdJp6ruZd1VAzyFzZy2Il8XMLLhc9GSPDiXApWiM57oK7DDiFA= =4Fmb -----END PGP SIGNATURE----- -- 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 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f45.google.com (mail-pa0-f45.google.com [209.85.220.45]) by kanga.kvack.org (Postfix) with ESMTP id 67FE66B0036 for ; Wed, 2 Oct 2013 13:15:39 -0400 (EDT) Received: by mail-pa0-f45.google.com with SMTP id rd3so1304188pab.32 for ; Wed, 02 Oct 2013 10:15:39 -0700 (PDT) Message-ID: <524C54B8.2060107@ubuntu.com> Date: Wed, 02 Oct 2013 13:15:36 -0400 From: Phillip Susi MIME-Version: 1.0 Subject: readahead man page incorrectly says it blocks Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: linux-mm@kvack.org -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 The man page for readahead(2) incorrectly claims that it blocks until all of the requested data has been read. I filed a bug a few months ago to have this corrected, but I think it is being ignored now because they don't believe me that it isn't supposed to block. Could someone help back me up and get this fixed? https://bugzilla.kernel.org/show_bug.cgi?id=54271 -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.17 (MingW32) Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQEcBAEBAgAGBQJSTFS4AAoJEJrBOlT6nu756hwIAJKQZnvazqLi8excUCrqc+HQ TSokhlBLBqRtk5nGN6X0UpDZ6KPFn0qsRpnhQApyk46nU/ru1YbbZLEtHgrWwaFW g2V+L248hIyYOYSAr/RCj9g4Zx5yMit6BOM1virD0VJ0cRDSA6mbNI0bVmTxEf+f 9UF2rwnXW63u3NwGjEMboVWCCOrfV3AGCTC31KTY/e2e1SUIlD8IIaRxW0RkVmVj PCmSVPvpaZoLaDgQ0F+sBBzLrCp9r72UT7j58Zzurj1GaIG2VEVAXKKij0b2Xtxg vjzflgrMd72pLhb+ppk/RP20FWmp6PJ3wKbK7zVrvILVHzSaoncDApURG/nBpHE= =zmD3 -----END PGP SIGNATURE----- -- 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 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f52.google.com (mail-pa0-f52.google.com [209.85.220.52]) by kanga.kvack.org (Postfix) with ESMTP id 562966B0062 for ; Wed, 2 Oct 2013 18:53:16 -0400 (EDT) Received: by mail-pa0-f52.google.com with SMTP id kl14so1677185pab.39 for ; Wed, 02 Oct 2013 15:53:16 -0700 (PDT) Date: Wed, 2 Oct 2013 18:53:10 -0400 From: Theodore Ts'o Subject: Re: readahead man page incorrectly says it blocks Message-ID: <20131002225310.GA12225@thunk.org> References: <524C54B8.2060107@ubuntu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <524C54B8.2060107@ubuntu.com> Sender: owner-linux-mm@kvack.org List-ID: To: Phillip Susi Cc: linux-mm@kvack.org On Wed, Oct 02, 2013 at 01:15:36PM -0400, Phillip Susi wrote: > > The man page for readahead(2) incorrectly claims that it blocks until > all of the requested data has been read. I filed a bug a few months > ago to have this corrected, but I think it is being ignored now > because they don't believe me that it isn't supposed to block. Could > someone help back me up and get this fixed? > > https://bugzilla.kernel.org/show_bug.cgi?id=54271 We do need to make sure that users of readahead(2) understand that: (a) readahead(2) *can* block (either to read metadata blocks, or perhaps due to a memory allocation from a kmalloc or get_free_page requiring pages to be cleaned and evicted) (b) readhead(2) does *not* guaranteee that once it returns, that a subsequent read or access to a mmap'ed page will not block. That is, readhead(2) does not block until the page becomes available in the page cache. BTW, Caveat (a) is also basically how AIO works --- io_submit(2) can block, which means that if thread was using AIO because it didn't want to lose control of the CPU, it can get quite disappointed. (With ext4 we have a way to preread and the file metadata and try very hard to keep it from getting ejected from memory to minimize this from happening, precisely because I had some users for which having io_submit(2) block was highly undesirable.) So you're right, but we do need to make sure that the resulting change doesn't cause the reader of the man page causes them to think that readhead(2) is guaranteeed not to block. Cheers, - Ted -- 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