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Fri, 15 Feb 2019 10:00:19 +0000 (UTC) Subject: Re: [PATCH 1/4] btrfs: Refactor cow_file_range_async To: linux-btrfs@vger.kernel.org References: <20190213155529.31500-1-nborisov@suse.com> <20190213155529.31500-2-nborisov@suse.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: <6ba18dd4-0344-682a-6002-2c02130e2925@suse.com> Date: Fri, 15 Feb 2019 12:00:16 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: <20190213155529.31500-2-nborisov@suse.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 13.02.19 г. 17:55 ч., Nikolay Borisov wrote: > This commit changes the implementation of cow_file_range_async in order > to get rid of the BUG_ON in the middle of the loop. Additionally it > reworks the inner loop in the hopes of making it more understandable. > > Main change is that the number of chunks required to handle the given > range is calculated before going into the loop and the logic of the loop > just iterates the chunk count. Furthermore, the way memory is allocated > is reworked and now the code does a single kmalloc with enough space to > handle all chunks. Depending on whether compression is enabled or not > chunks are either 1 (in non-compress case) or the range divided by 512k. > > Signed-off-by: Nikolay Borisov Scratch that patch since it could lead to deadlocks. It's not enough to just return an error and hop higher levels will unlock the pages and whatnot. Other callers (cow_file_range/run_delalloc_nocow) use extent_clear_unlock_delalloc. > --- > fs/btrfs/inode.c | 75 +++++++++++++++++++++++++++++++----------------- > 1 file changed, 49 insertions(+), 26 deletions(-) > > diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c > index 05bbfd02ea49..c2180f0a5f42 100644 > --- a/fs/btrfs/inode.c > +++ b/fs/btrfs/inode.c > @@ -375,6 +375,7 @@ struct async_cow { > unsigned int write_flags; > struct list_head extents; > struct btrfs_work work; > + atomic_t *pending; > }; > > static noinline int add_async_extent(struct async_cow *cow, > @@ -1181,7 +1182,12 @@ static noinline void async_cow_free(struct btrfs_work *work) > async_cow = container_of(work, struct async_cow, work); > if (async_cow->inode) > btrfs_add_delayed_iput(async_cow->inode); > - kfree(async_cow); > + /* > + * Since the pointer to 'pending' is at the beginning of the array of > + * async_cow's, freeing it ensures the whole array has been freed. > + */ > + if (atomic_dec_and_test(async_cow->pending)) > + kfree(async_cow->pending); > } > > static int cow_file_range_async(struct inode *inode, struct page *locked_page, > @@ -1193,42 +1199,59 @@ static int cow_file_range_async(struct inode *inode, struct page *locked_page, > struct async_cow *async_cow; > unsigned long nr_pages; > u64 cur_end; > + u64 num_chunks = DIV_ROUND_UP(end - start, SZ_512K); > + int i; > + bool should_compress; > + atomic_t *p; > + > > clear_extent_bit(&BTRFS_I(inode)->io_tree, start, end, EXTENT_LOCKED, > 1, 0, NULL); > - while (start < end) { > - async_cow = kmalloc(sizeof(*async_cow), GFP_NOFS); > - BUG_ON(!async_cow); /* -ENOMEM */ > - /* > - * igrab is called higher up in the call chain, take only the > - * lightweight reference for the callback lifetime > - */ > - ihold(inode); > - async_cow->inode = inode; > - async_cow->fs_info = fs_info; > - async_cow->locked_page = locked_page; > - async_cow->start = start; > - async_cow->write_flags = write_flags; > - > - if (BTRFS_I(inode)->flags & BTRFS_INODE_NOCOMPRESS && > - !btrfs_test_opt(fs_info, FORCE_COMPRESS)) > - cur_end = end; > - else > - cur_end = min(end, start + SZ_512K - 1); > > - async_cow->end = cur_end; > - INIT_LIST_HEAD(&async_cow->extents); > + if (BTRFS_I(inode)->flags & BTRFS_INODE_NOCOMPRESS && > + !btrfs_test_opt(fs_info, FORCE_COMPRESS)) { > + num_chunks = 1; > + should_compress = false; > + } else { > + should_compress = true; > + } > + > + /* Layout is [atomic_t][async_cow1][async_cowN].... */ > + async_cow = kmalloc(sizeof(atomic_t) + num_chunks*sizeof(*async_cow), > + GFP_NOFS); > + if (!async_cow) > + return -ENOMEM; > + > + p = (atomic_t *)async_cow; > + async_cow = (struct async_cow *)((char *)async_cow + sizeof(atomic_t)); > + atomic_set(p, num_chunks); > + > + for (i = 0; i < num_chunks; i++) { > > - btrfs_init_work(&async_cow->work, > + if (should_compress) > + cur_end = min(end, start + SZ_512K - 1); > + else > + cur_end = end; > + > + ihold(inode); > + async_cow[i].pending= p; > + async_cow[i].inode = inode; > + async_cow[i].start = start; > + async_cow[i].end = cur_end; > + async_cow[i].fs_info = fs_info; > + async_cow[i].locked_page = locked_page; > + async_cow[i].write_flags = write_flags; > + INIT_LIST_HEAD(&async_cow[i].extents); > + > + btrfs_init_work(&async_cow[i].work, > btrfs_delalloc_helper, > async_cow_start, async_cow_submit, > async_cow_free); > > - nr_pages = (cur_end - start + PAGE_SIZE) >> > - PAGE_SHIFT; > + nr_pages = DIV_ROUND_UP(cur_end - start, PAGE_SIZE); > atomic_add(nr_pages, &fs_info->async_delalloc_pages); > > - btrfs_queue_work(fs_info->delalloc_workers, &async_cow->work); > + btrfs_queue_work(fs_info->delalloc_workers, &async_cow[i].work); > > *nr_written += nr_pages; > start = cur_end + 1; >