From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Moyer Subject: Re: Revert "aio: block exit_aio() until all context requests are completed" Date: Fri, 15 May 2015 09:42:17 -0400 Message-ID: References: <1431675417-30464-1-git-send-email-borntraeger@de.ibm.com> <5555A33B.20006@de.ibm.com> Mime-Version: 1.0 Content-Type: text/plain Cc: Gu Zheng , Benjamin LaHaise , linux-aio@kvack.org, linux-fsdevel@vger.kernel.org To: Christian Borntraeger Return-path: Received: from mx1.redhat.com ([209.132.183.28]:49899 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1422697AbbEONm2 (ORCPT ); Fri, 15 May 2015 09:42:28 -0400 In-Reply-To: <5555A33B.20006@de.ibm.com> (Christian Borntraeger's message of "Fri, 15 May 2015 09:41:47 +0200") Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Christian Borntraeger writes: > I see a significant latency (can be minutes with 2000 disks and HZ=100) > when exiting a QEMU process that has lots of disk devices via aio. The > process sits idle doing nothing as zombie in exit_aio waiting for the > completion. > > Turns out that > commit 6098b45b32 ("aio: block exit_aio() until all context requests are > completed") caused the delay. > > Patch description was: > > It seems that exit_aio() also needs to wait for all iocbs to complete (like > io_destroy), but we missed the wait step in current implemention, so fix > it in the same way as we did in io_destroy. > > Now: io_destroy requires to block until everything is cleaned up from its > interface description in the manpage: > DESCRIPTION > The io_destroy() system call will attempt to cancel all outstanding > asynchronous I/O operations against ctx_id, will block on the completion > of all operations that could not be canceled, and will destroy the ctx_id. > > Does process exit require the same full blocking? We might be able to > cleanup the process and let the aio data structures be freed lazily. > Opinions or better ideas? This has already been fixed: commit dc48e56d761610da4ea1088d1bea0a030b8e3e43 Author: Jens Axboe Date: Wed Apr 15 11:17:23 2015 -0600 aio: fix serial draining in exit_aio() Cheers, Jeff