From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D3D12C3A5A2 for ; Fri, 23 Aug 2019 07:48:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A828A22CE3 for ; Fri, 23 Aug 2019 07:48:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390902AbfHWHsp (ORCPT ); Fri, 23 Aug 2019 03:48:45 -0400 Received: from mx2.suse.de ([195.135.220.15]:35046 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728519AbfHWHsp (ORCPT ); Fri, 23 Aug 2019 03:48:45 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 6EEABAECA; Fri, 23 Aug 2019 07:48:42 +0000 (UTC) Subject: Re: [PATCH 4/9] btrfs: rework btrfs_space_info_add_old_bytes To: Josef Bacik , kernel-team@fb.com, linux-btrfs@vger.kernel.org References: <20190822191102.13732-1-josef@toxicpanda.com> <20190822191102.13732-5-josef@toxicpanda.com> From: Nikolay Borisov Openpgp: preference=signencrypt Autocrypt: addr=nborisov@suse.com; prefer-encrypt=mutual; keydata= mQINBFiKBz4BEADNHZmqwhuN6EAzXj9SpPpH/nSSP8YgfwoOqwrP+JR4pIqRK0AWWeWCSwmZ T7g+RbfPFlmQp+EwFWOtABXlKC54zgSf+uulGwx5JAUFVUIRBmnHOYi/lUiE0yhpnb1KCA7f u/W+DkwGerXqhhe9TvQoGwgCKNfzFPZoM+gZrm+kWv03QLUCr210n4cwaCPJ0Nr9Z3c582xc bCUVbsjt7BN0CFa2BByulrx5xD9sDAYIqfLCcZetAqsTRGxM7LD0kh5WlKzOeAXj5r8DOrU2 GdZS33uKZI/kZJZVytSmZpswDsKhnGzRN1BANGP8sC+WD4eRXajOmNh2HL4P+meO1TlM3GLl EQd2shHFY0qjEo7wxKZI1RyZZ5AgJnSmehrPCyuIyVY210CbMaIKHUIsTqRgY5GaNME24w7h TyyVCy2qAM8fLJ4Vw5bycM/u5xfWm7gyTb9V1TkZ3o1MTrEsrcqFiRrBY94Rs0oQkZvunqia c+NprYSaOG1Cta14o94eMH271Kka/reEwSZkC7T+o9hZ4zi2CcLcY0DXj0qdId7vUKSJjEep c++s8ncFekh1MPhkOgNj8pk17OAESanmDwksmzh1j12lgA5lTFPrJeRNu6/isC2zyZhTwMWs k3LkcTa8ZXxh0RfWAqgx/ogKPk4ZxOXQEZetkEyTFghbRH2BIwARAQABtCNOaWtvbGF5IEJv cmlzb3YgPG5ib3Jpc292QHN1c2UuY29tPokCOAQTAQIAIgUCWIo48QIbAwYLCQgHAwIGFQgC CQoLBBYCAwECHgECF4AACgkQcb6CRuU/KFc0eg/9GLD3wTQz9iZHMFbjiqTCitD7B6dTLV1C ddZVlC8Hm/TophPts1bWZORAmYIihHHI1EIF19+bfIr46pvfTu0yFrJDLOADMDH+Ufzsfy2v HSqqWV/nOSWGXzh8bgg/ncLwrIdEwBQBN9SDS6aqsglagvwFD91UCg/TshLlRxD5BOnuzfzI Leyx2c6YmH7Oa1R4MX9Jo79SaKwdHt2yRN3SochVtxCyafDlZsE/efp21pMiaK1HoCOZTBp5 VzrIP85GATh18pN7YR9CuPxxN0V6IzT7IlhS4Jgj0NXh6vi1DlmKspr+FOevu4RVXqqcNTSS E2rycB2v6cttH21UUdu/0FtMBKh+rv8+yD49FxMYnTi1jwVzr208vDdRU2v7Ij/TxYt/v4O8 V+jNRKy5Fevca/1xroQBICXsNoFLr10X5IjmhAhqIH8Atpz/89ItS3+HWuE4BHB6RRLM0gy8 T7rN6ja+KegOGikp/VTwBlszhvfLhyoyjXI44Tf3oLSFM+8+qG3B7MNBHOt60CQlMkq0fGXd mm4xENl/SSeHsiomdveeq7cNGpHi6i6ntZK33XJLwvyf00PD7tip/GUj0Dic/ZUsoPSTF/mG EpuQiUZs8X2xjK/AS/l3wa4Kz2tlcOKSKpIpna7V1+CMNkNzaCOlbv7QwprAerKYywPCoOSC 7P25Ag0EWIoHPgEQAMiUqvRBZNvPvki34O/dcTodvLSyOmK/MMBDrzN8Cnk302XfnGlW/YAQ csMWISKKSpStc6tmD+2Y0z9WjyRqFr3EGfH1RXSv9Z1vmfPzU42jsdZn667UxrRcVQXUgoKg QYx055Q2FdUeaZSaivoIBD9WtJq/66UPXRRr4H/+Y5FaUZx+gWNGmBT6a0S/GQnHb9g3nonD jmDKGw+YO4P6aEMxyy3k9PstaoiyBXnzQASzdOi39BgWQuZfIQjN0aW+Dm8kOAfT5i/yk59h VV6v3NLHBjHVw9kHli3jwvsizIX9X2W8tb1SefaVxqvqO1132AO8V9CbE1DcVT8fzICvGi42 FoV/k0QOGwq+LmLf0t04Q0csEl+h69ZcqeBSQcIMm/Ir+NorfCr6HjrB6lW7giBkQl6hhomn l1mtDP6MTdbyYzEiBFcwQD4terc7S/8ELRRybWQHQp7sxQM/Lnuhs77MgY/e6c5AVWnMKd/z MKm4ru7A8+8gdHeydrRQSWDaVbfy3Hup0Ia76J9FaolnjB8YLUOJPdhI2vbvNCQ2ipxw3Y3c KhVIpGYqwdvFIiz0Fej7wnJICIrpJs/+XLQHyqcmERn3s/iWwBpeogrx2Lf8AGezqnv9woq7 OSoWlwXDJiUdaqPEB/HmGfqoRRN20jx+OOvuaBMPAPb+aKJyle8zABEBAAGJAh8EGAECAAkF AliKBz4CGwwACgkQcb6CRuU/KFdacg/+M3V3Ti9JYZEiIyVhqs+yHb6NMI1R0kkAmzsGQ1jU zSQUz9AVMR6T7v2fIETTT/f5Oout0+Hi9cY8uLpk8CWno9V9eR/B7Ifs2pAA8lh2nW43FFwp IDiSuDbH6oTLmiGCB206IvSuaQCp1fed8U6yuqGFcnf0ZpJm/sILG2ECdFK9RYnMIaeqlNQm iZicBY2lmlYFBEaMXHoy+K7nbOuizPWdUKoKHq+tmZ3iA+qL5s6Qlm4trH28/fPpFuOmgP8P K+7LpYLNSl1oQUr+WlqilPAuLcCo5Vdl7M7VFLMq4xxY/dY99aZx0ZJQYFx0w/6UkbDdFLzN upT7NIN68lZRucImffiWyN7CjH23X3Tni8bS9ubo7OON68NbPz1YIaYaHmnVQCjDyDXkQoKC R82Vf9mf5slj0Vlpf+/Wpsv/TH8X32ajva37oEQTkWNMsDxyw3aPSps6MaMafcN7k60y2Wk/ TCiLsRHFfMHFY6/lq/c0ZdOsGjgpIK0G0z6et9YU6MaPuKwNY4kBdjPNBwHreucrQVUdqRRm RcxmGC6ohvpqVGfhT48ZPZKZEWM+tZky0mO7bhZYxMXyVjBn4EoNTsXy1et9Y1dU3HVJ8fod 5UqrNrzIQFbdeM0/JqSLrtlTcXKJ7cYFa9ZM2AP7UIN9n1UWxq+OPY9YMOewVfYtL8M= Message-ID: Date: Fri, 23 Aug 2019 10:48:35 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190822191102.13732-5-josef@toxicpanda.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 22.08.19 г. 22:10 ч., Josef Bacik wrote: > If there are pending tickets and we are overcommitted we will simply > return free'd reservations to space_info->bytes_may_use if we cannot > overcommit any more. This is problematic because we assume any free > space would have been added to the tickets, and so if we go from an > overcommitted state to not overcommitted we could have plenty of space > in our space_info but be unable to make progress on our tickets because > we only refill tickets from previous reservations. > > Consider the following example. We were allowed to overcommit to > space_info->total_bytes + 2mib. Now we've allocated all of our chunks > and are no longer allowed to overcommit those extra 2mib. Assume there > is a 3mib reservation we are now freeing. Because we can no longer > overcommit we do not partially refill the ticket with the 3mib, instead > we subtract it from space_info->bytes_may_use. Now the total reserved > space is 1mib less than total_bytes, meaning we have 1mib of space we > could reserve. Now assume that our ticket is 2mib, and we only have > 1mib of space to reclaim, so we have a partial refilling to 1mib. We > keep trying to flush and eventually give up and ENOSPC the ticket, when > there was the remaining 1mib left in the space_info for usage. The wording of this paragraph makes it a bit hard to understand. How about something like: Consider an example where a request is allowed to overcommit space_info->total_bytes + 2mib. At this point it's no longer possible to overcommit extra space. At the same time there is an existing 3mib reservation which is being freed. Due to the existing check failing: if (check_overcommit && !can_overcommit(fs_info, space_info, 0, flush, false)) btrfs_space_info_add_old_bytes won't partially refill tickets with those 3mib, instead it will subtract them from space_info->bytes_may_use. This results in the total reserved space being 1mib below space_info->total_bytes. total_bytes> > > Instead of doing this partial filling of tickets dance we need to simply > add our space to the space_info, and then do the normal check to see if > we can satisfy the whole reservation. If we can then we wake up the > ticket and carry on. This solves the above problem and makes it much > more straightforward to understand how the tickets are satisfied. > > Signed-off-by: Josef Bacik > --- > fs/btrfs/space-info.c | 43 ++++++++++++++++--------------------------- > 1 file changed, 16 insertions(+), 27 deletions(-) > > diff --git a/fs/btrfs/space-info.c b/fs/btrfs/space-info.c > index a0a36d5768e1..357fe7548e07 100644 > --- a/fs/btrfs/space-info.c > +++ b/fs/btrfs/space-info.c > @@ -233,52 +233,41 @@ void btrfs_space_info_add_old_bytes(struct btrfs_fs_info *fs_info, > struct btrfs_space_info *space_info, > u64 num_bytes) > { > - struct reserve_ticket *ticket; > struct list_head *head; > - u64 used; > enum btrfs_reserve_flush_enum flush = BTRFS_RESERVE_NO_FLUSH; > - bool check_overcommit = false; > > spin_lock(&space_info->lock); > head = &space_info->priority_tickets; > + btrfs_space_info_update_bytes_may_use(fs_info, space_info, -num_bytes); > > - /* > - * If we are over our limit then we need to check and see if we can > - * overcommit, and if we can't then we just need to free up our space > - * and not satisfy any requests. > - */ > - used = btrfs_space_info_used(space_info, true); > - if (used - num_bytes >= space_info->total_bytes) > - check_overcommit = true; > again: > - while (!list_empty(head) && num_bytes) { > - ticket = list_first_entry(head, struct reserve_ticket, > - list); > - /* > - * We use 0 bytes because this space is already reserved, so > - * adding the ticket space would be a double count. > - */ > - if (check_overcommit && > - !can_overcommit(fs_info, space_info, 0, flush, false)) > - break; > - if (num_bytes >= ticket->bytes) { > + while (!list_empty(head)) { > + struct reserve_ticket *ticket; > + u64 used = btrfs_space_info_used(space_info, true); > + > + ticket = list_first_entry(head, struct reserve_ticket, list); > + > + /* Check and see if our ticket can be satisified now. */ > + if ((used + ticket->bytes <= space_info->total_bytes) || > + can_overcommit(fs_info, space_info, ticket->bytes, flush, > + false)) { > + btrfs_space_info_update_bytes_may_use(fs_info, > + space_info, > + ticket->bytes); > list_del_init(&ticket->list); > - num_bytes -= ticket->bytes; > ticket->bytes = 0; > space_info->tickets_id++; > wake_up(&ticket->wait); > } else { > - ticket->bytes -= num_bytes; > - num_bytes = 0; > + break; > } > } > > - if (num_bytes && head == &space_info->priority_tickets) { > + if (head == &space_info->priority_tickets) { > head = &space_info->tickets; > flush = BTRFS_RESERVE_FLUSH_ALL; > goto again; > } > - btrfs_space_info_update_bytes_may_use(fs_info, space_info, -num_bytes); > spin_unlock(&space_info->lock); > } > >