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[174.109.172.136]) by smtp.gmail.com with ESMTPSA id e189sm1485856qkf.24.2021.01.27.08.17.58 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 27 Jan 2021 08:17:58 -0800 (PST) Subject: Re: [PATCH v5 00/18] btrfs: add read-only support for subpage sector size To: Qu Wenruo , linux-btrfs@vger.kernel.org References: <20210126083402.142577-1-wqu@suse.com> From: Josef Bacik Message-ID: Date: Wed, 27 Jan 2021 11:17:57 -0500 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.6.1 MIME-Version: 1.0 In-Reply-To: <20210126083402.142577-1-wqu@suse.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 1/26/21 3:33 AM, Qu Wenruo wrote: > Patches can be fetched from github: > https://github.com/adam900710/linux/tree/subpage > Currently the branch also contains partial RW data support (still some > ordered extent and data csum mismatch problems) > > Great thanks to David/Nikolay/Josef for their effort reviewing and > merging the preparation patches into misc-next. > > === What works === > Just from the patchset: > - Data read > Both regular and compressed data, with csum check. > > - Metadata read > > This means, with these patchset, 64K page systems can at least mount > btrfs with 4K sector size read-only. > This should provide the ability to migrate data at least. > > While on the github branch, there are already experimental RW supports, > there are still ordered extent related bugs for me to fix. > Thus only the RO part is sent for review and testing. > > === Patchset structure === > Patch 01~02: Preparation patches which don't have functional change > Patch 03~12: Subpage metadata allocation and freeing > Patch 13~15: Subpage metadata read path > Patch 16~17: Subpage data read path > Patch 18: Enable subpage RO support > > === Changelog === > v1: > - Separate the main implementation from previous huge patchset > Huge patchset doesn't make much sense. > > - Use bitmap implementation > Now page::private will be a pointer to btrfs_subpage structure, which > contains bitmaps for various page status. > > v2: > - Use page::private as btrfs_subpage for extra info > This replace old extent io tree based solution, which reduces latency > and don't require memory allocation for its operations. > > - Cherry-pick new preparation patches from RW development > Those new preparation patches improves the readability by their own. > > v3: > - Make dummy extent buffer to follow the same subpage accessors > Fsstress exposed several ASSERT() for dummy extent buffers. > It turns out we need to make dummy extent buffer to own the same > btrfs_subpage structure to make eb accessors to work properly > > - Two new small __process_pages_contig() related preparation patches > One to make __process_pages_contig() to enhance the error handling > path for locked_page, one to merge one macro. > > - Extent buffers refs count update > Except try_release_extent_buffer(), all other eb uses will try to > increase the ref count of the eb. > For try_release_extent_buffer(), the eb refs check will happen inside > the rcu critical section to avoid eb being freed. > > - Comment updates > Addressing the comments from the mail list. > > v4: > - Get rid of btrfs_subpage::tree_block_bitmap > This is to reduce lock complexity (no need to bother extra subpage > lock for metadata, all locks are existing locks) > Now eb looking up mostly depends on radix tree, with small help from > btrfs_subpage::under_alloc. > Now I haven't experieneced metadata related problems any more during > my local fsstress tests. > > - Fix a race where metadata page dirty bit can race > Fixed in the metadata RW patchset though. > > - Rebased to latest misc-next branch > With 4 patches removed, as they are already in misc-next. > > v5: > - Use the updated version from David as base > Most comment/commit message update should be kept as is. > > - A new separate patch to move UNMAPPED bit set timing > > - New comment on why we need to prealloc subpage inside a loop > Mostly for further 16K page size support, where we can have > eb across multiple pages. > > - Remove one patch which is too RW specific > Since it introduces functional change which only makes sense for RW > support, it's not a good idea to include it in RO support. > > - Error handling fixes > Great thanks to Josef. > > - Refactor btrfs_subpage allocation/freeing > Now we have btrfs_alloc_subpage() and btrfs_free_subpage() helpers to > do all the allocation/freeing. > It's pretty easy to convert to kmem_cache using above helpers. > (already internally tested using kmem_cache without problem, in fact > it's all the problems found in kmem_cache test leads to the new > interface) > > - Use btrfs_subpage::eb_refs to replace old under_alloc > This makes checking whether the page has any eb left much easier. > > Qu Wenruo (18): > btrfs: merge PAGE_CLEAR_DIRTY and PAGE_SET_WRITEBACK to > PAGE_START_WRITEBACK > btrfs: set UNMAPPED bit early in btrfs_clone_extent_buffer() for > subpage support > btrfs: introduce the skeleton of btrfs_subpage structure > btrfs: make attach_extent_buffer_page() handle subpage case > btrfs: make grab_extent_buffer_from_page() handle subpage case > btrfs: support subpage for extent buffer page release I don't have this patch in my inbox so I can't reply to it directly, but you include refcount.h, but then use normal atomics. Please used the actual refcount_t, as it gets us all the debugging stuff that makes finding problems much easier. Thanks, Josef