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path: root/drivers/md/bitmap.c
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2015-10-12md-cluster: Use a small window for resyncGoldwyn Rodrigues1-2/+2
Suspending the entire device for resync could take too long. Resync in small chunks. cluster's resync window (32M) is maintained in r1conf as cluster_sync_low and cluster_sync_high and processed in raid1's sync_request(). If the current resync is outside the cluster resync window: 1. Set the cluster_sync_low to curr_resync_completed. 2. Check if the sync will fit in the new window, if not issue a wait_barrier() and set cluster_sync_low to sector_nr. 3. Set cluster_sync_high to cluster_sync_low + resync_window. 4. Send a message to all nodes so they may add it in their suspension list. bitmap_cond_end_sync is modified to allow to force a sync inorder to get the curr_resync_completed uptodate with the sector passed. Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com> Signed-off-by: NeilBrown <neilb@suse.de>
2015-10-12md: Increment version for clustered bitmapsGoldwyn Rodrigues1-6/+4
Add BITMAP_MAJOR_CLUSTERED as 5, in order to prevent older kernels to assemble a clustered device. In order to maximize compatibility, the major version is set to BITMAP_MAJOR_CLUSTERED *only* if the bitmap is clustered. Added MD_FEATURE_CLUSTERED in order to return error for older kernels which would assemble MD even if the bitmap is corrupted. Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com> Signed-off-by: NeilBrown <neilb@suse.com>
2015-10-02md/bitmap: don't pass -1 to bitmap_storage_alloc.NeilBrown1-1/+2
Passing -1 to bitmap_storage_alloc() causes page->index to be set to -1, which is quite problematic. So only pass ->cluster_slot if mddev_is_clustered(). Fixes: b97e92574c0b ("Use separate bitmaps for each nodes in the cluster") Cc: stable@vger.kernel.org (v4.1+) Signed-off-by: NeilBrown <neilb@suse.com>
2015-07-25Merge tag 'md/4.2-fixes' of git://neil.brown.name/mdLinus Torvalds1-11/+17
Pull md fixes from Neil Brown: "Some md fixes for 4.2 Several are tagged for -stable. A few aren't because they are not very, serious or because they are in the 'experimental' cluster code" * tag 'md/4.2-fixes' of git://neil.brown.name/md: md/raid5: clear R5_NeedReplace when no longer needed. Fix read-balancing during node failure md-cluster: fix bitmap sub-offset in bitmap_read_sb md: Return error if request_module fails and returns positive value md: Skip cluster setup in case of error while reading bitmap md/raid1: fix test for 'was read error from last working device'. md: Skip cluster setup for dm-raid md: flush ->event_work before stopping array. md/raid10: always set reshape_safe when initializing reshape_position. md/raid5: avoid races when changing cache size.
2015-07-24md-cluster: fix bitmap sub-offset in bitmap_read_sbGoldwyn Rodrigues1-7/+4
bitmap_read_sb is modifying mddev->bitmap_info.offset. This works for the first bitmap read. However, when multiple bitmaps need to be opened by the same node, it ends up corrupting the offset. Fix it by using a local variable. Also, bitmap_read_sb is not required in bitmap_copy_from_slot since it is called in bitmap_create. Remove bitmap_read_sb(). Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com> Signed-off-by: NeilBrown <neilb@suse.com>
2015-07-24md: Skip cluster setup in case of error while reading bitmapGoldwyn Rodrigues1-1/+1
If the bitmap read fails, the error code set is -EINVAL. However, we don't check for errors and go ahead with cluster_setup. Skip the cluster setup in case of error. Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com> Signed-off-by: NeilBrown <neilb@suse.com>
2015-07-23md: Skip cluster setup for dm-raidGoldwyn Rodrigues1-3/+12
There is a bug that the bitmap superblock isn't initialised properly for dm-raid, so a new field can have garbage in new fields. (dm-raid does initialisation in the kernel - md initialised the superblock in mdadm). This means that for dm-raid we cannot currently trust the new ->nodes field. So: - use __GFP_ZERO to initialise the superblock properly for all new arrays - initialise all fields in bitmap_info in bitmap_new_disk_sb - ignore ->nodes for dm arrays (yes, this is a hack) This bug exposes dm-raid to bug in the (still experimental) md-cluster code, so it is suitable for -stable. It does cause crashes. References: https://bugzilla.kernel.org/show_bug.cgi?id=100491 Cc: stable@vger.kernel.org (v4.1) Signed-off-By: Goldwyn Rodrigues <rgoldwyn@suse.com> Signed-off-by: NeilBrown <neilb@suse.com>
2015-07-05Merge branch 'for-linus' of ↵Linus Torvalds1-2/+2
git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs Pull more vfs updates from Al Viro: "Assorted VFS fixes and related cleanups (IMO the most interesting in that part are f_path-related things and Eric's descriptor-related stuff). UFS regression fixes (it got broken last cycle). 9P fixes. fs-cache series, DAX patches, Jan's file_remove_suid() work" [ I'd say this is much more than "fixes and related cleanups". The file_table locking rule change by Eric Dumazet is a rather big and fundamental update even if the patch isn't huge. - Linus ] * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (49 commits) 9p: cope with bogus responses from server in p9_client_{read,write} p9_client_write(): avoid double p9_free_req() 9p: forgetting to cancel request on interrupted zero-copy RPC dax: bdev_direct_access() may sleep block: Add support for DAX reads/writes to block devices dax: Use copy_from_iter_nocache dax: Add block size note to documentation fs/file.c: __fget() and dup2() atomicity rules fs/file.c: don't acquire files->file_lock in fd_install() fs:super:get_anon_bdev: fix race condition could cause dev exceed its upper limitation vfs: avoid creation of inode number 0 in get_next_ino namei: make set_root_rcu() return void make simple_positive() public ufs: use dir_pages instead of ufs_dir_pages() pagemap.h: move dir_pages() over there remove the pointless include of lglock.h fs: cleanup slight list_entry abuse xfs: Correctly lock inode when removing suid and file capabilities fs: Call security_ops->inode_killpriv on truncate fs: Provide function telling whether file_remove_privs() will do anything ...
2015-06-24vfs: add seq_file_path() helperMiklos Szeredi1-1/+1
Turn seq_path(..., &file->f_path, ...); into seq_file_path(..., file, ...); Signed-off-by: Miklos Szeredi <mszeredi@suse.cz> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2015-06-24vfs: add file_path() helperMiklos Szeredi1-1/+1
Turn d_path(&file->f_path, ...); into file_path(file, ...); Signed-off-by: Miklos Szeredi <mszeredi@suse.cz> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2015-05-21md/bitmap: remove rcu annotation from pointer arithmetic.NeilBrown1-1/+6
Evaluating "&mddev->disks" is simple pointer arithmetic, so it does not need 'rcu' annotations - no dereferencing is happening. Also enhance the comment to explain that 'rdev' in that case is not actually a pointer to an rdev. Reported-by: Patrick Marlier <patrick.marlier@gmail.com> Signed-off-by: NeilBrown <neilb@suse.de>
2015-04-22md-cluster: re-add capabilitiesGoldwyn Rodrigues1-9/+11
When "re-add" is writted to /sys/block/mdXX/md/dev-YYY/state, the clustered md: 1. Sends RE_ADD message with the desc_nr. Nodes receiving the message clear the Faulty bit in their respective rdev->flags. 2. The node initiating re-add, gathers the bitmaps of all nodes and copies them into the local bitmap. It does not clear the bitmap from which it is copying. 3. Initiating node schedules a md recovery to sync the devices. Signed-off-by: Guoqing Jiang <gqjiang@suse.com> Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com> Signed-off-by: NeilBrown <neilb@suse.de>
2015-03-25md: Fix bitmap offset calculationsGoldwyn Rodrigues1-4/+3
The calculations of bitmap offset is incorrect with respect to bits to bytes conversion. Also, remove an irrelevant duplicate message. Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com> Signed-off-by: NeilBrown <neilb@suse.de>
2015-03-04md/bitmap: use sector_div for sector_t divisionsStephen Rothwell1-2/+3
neilb: modified to not corrupt ->resync_max_sectors. sector_div usage fixed by Guoqing Jiang <gqjiang@suse.com> Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au> Signed-off-by: NeilBrown <neilb@suse.de>
2015-03-04md/bitmap: fix incorrect DIV_ROUND_UP usage.NeilBrown1-2/+2
DIV_ROUTND_UP doesn't work on "long long", - and it should be sector_t anyway. Signed-off-by: NeilBrown <neilb@suse.de>
2015-02-23Copy set bits from another slotGoldwyn Rodrigues1-1/+77
bitmap_copy_from_slot reads the bitmap from the slot mentioned. It then copies the set bits to the node local bitmap. This is helper function for the resync operation on node failure. bitmap_set_memory_bits() currently assumes it is only run at startup and that they bitmap is currently empty. So if it finds that a region is already marked as dirty, it won't mark it dirty again. Change bitmap_set_memory_bits() to always set the NEEDED_MASK bit if 'needed' is set. Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
2015-02-23bitmap_create returns bitmap pointerGoldwyn Rodrigues1-24/+36
This is done to have multiple bitmaps open at the same time. Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
2015-02-23Use separate bitmaps for each nodes in the clusterGoldwyn Rodrigues1-10/+57
On-disk format: 0 4k 8k 12k ------------------------------------------------------------------- | idle | md super | bm super [0] + bits | | bm bits[0, contd] | bm super[1] + bits | bm bits[1, contd] | | bm super[2] + bits | bm bits [2, contd] | bm super[3] + bits | | bm bits [3, contd] | | | Bitmap super has a field nodes, which defines the maximum number of nodes the device can use. While reading the bitmap super, if the cluster finds out that the number of nodes is > 0: 1. Requests the md-cluster module. 2. Calls md_cluster_ops->join(), which sets up clustering such as joining DLM lockspace. Since the first time, the first bitmap is read. After the call to the cluster_setup, the bitmap offset is adjusted and the superblock is re-read. This also ensures the bitmap is read the bitmap lock (when bitmap lock is introduced in later patches) Questions: 1. cluster name is repeated in all bitmap supers. Is that okay? Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
2015-02-23Add node recovery callbacksGoldwyn Rodrigues1-0/+1
DLM offers callbacks when a node fails and the lock remastery is performed: 1. recover_prep: called when DLM discovers a node is down 2. recover_slot: called when DLM identifies the node and recovery can start 3. recover_done: called when all nodes have completed recover_slot recover_slot() and recover_done() are also called when the node joins initially in order to inform the node with its slot number. These slot numbers start from one, so we deduct one to make it start with zero which the cluster-md code uses. Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
2015-02-23Introduce md_cluster_infoGoldwyn Rodrigues1-1/+8
md_cluster_info stores the cluster information in the MD device. The join() is called when mddev detects it is a clustered device. The main responsibilities are: 1. Setup a DLM lockspace 2. Setup all initial locks such as super block locks and bitmap lock (will come later) The leave() clears up the lockspace and all the locks held. Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
2015-02-06md: remove mddev_lock() from md_attr_show()NeilBrown1-3/+10
Most attributes can be read safely without any locking. A race might lead to a slightly out-dated value, but nothing wrong. We already have locking in some places where needed. All that remains is can_clear_show(), behind_writes_used_show() and action_show() which are easily fixed. Signed-off-by: NeilBrown <neilb@suse.de>
2015-02-06md/bitmap: protect clearing of ->bitmap by mddev->lockNeilBrown1-0/+2
This makes it safe to inspect the struct while holding only the spinlock. Signed-off-by: NeilBrown <neilb@suse.de>
2015-02-02md/bitmap: fix a might_sleep() warning.NeilBrown1-0/+13
commit 8eb23b9f35aae413140d3fda766a98092c21e9b0 sched: Debug nested sleeps causes false-positive warnings in RAID5 code. This annotation removes them and adds a comment explaining why there is no real problem. Reported-by: Fengguang Wu <fengguang.wu@intel.com> Signed-off-by: NeilBrown <neilb@suse.de>
2014-10-09md/bitmap: always wait for writes on unplug.NeilBrown1-10/+6
If two threads call bitmap_unplug at the same time, then one might schedule all the writes, and the other might decide that it doesn't need to wait. But really it does. It rarely hurts to wait when it isn't absolutely necessary, and the current code doesn't really focus on 'absolutely necessary' anyway. So just wait always. This can potentially lead to data corruption if a crash happens at an awkward time and data was written before the bitmap was updated. It is very unlikely, but this should go to -stable just to be safe. Appropriate for any -stable. Signed-off-by: NeilBrown <neilb@suse.de> Cc: stable@vger.kernel.org (please delay until 3.18 is released)
2014-05-29md/bitmap: remove confusing code from filemap_get_page.NeilBrown1-5/+1
file_page_index(store, 0) is *always* 0. This is because the bitmap sb, at 256 bytes, is *always* less than one page. So subtracting it has no effect and the code should be removed. Reported-by: Goldwyn Rodrigues <rgoldwyn@suse.de> Signed-off-by: NeilBrown <neilb@suse.de>
2014-04-09md/bitmap: don't abuse i_writecount for bitmap files.NeilBrown1-1/+0
md bitmap code currently tries to use i_writecount to stop any other process from writing to out bitmap file. But that is really an abuse and has bit-rotted so locking is all wrong. So discard that - root should be allowed to shoot self in foot. Still use it in a much less intrusive way to stop the same file being used as bitmap on two different array, and apply other checks to ensure the file is at least vaguely usable for bitmap storage (is regular, is open for write. Support for ->bmap is already checked elsewhere). Reported-by: Al Viro <viro@ZenIV.linux.org.uk> Signed-off-by: NeilBrown <neilb@suse.de>
2013-12-12kernfs: s/sysfs_dirent/kernfs_node/ and rename its friends accordinglyTejun Heo1-1/+1
kernfs has just been separated out from sysfs and we're already in full conflict mode. Nothing can make the situation any worse. Let's take the chance to name things properly. This patch performs the following renames. * s/sysfs_elem_dir/kernfs_elem_dir/ * s/sysfs_elem_symlink/kernfs_elem_symlink/ * s/sysfs_elem_attr/kernfs_elem_file/ * s/sysfs_dirent/kernfs_node/ * s/sd/kn/ in kernfs proper * s/parent_sd/parent/ * s/target_sd/target/ * s/dir_sd/parent/ * s/to_sysfs_dirent()/rb_to_kn()/ * misc renames of local vars when they conflict with the above Because md, mic and gpio dig into sysfs details, this patch ends up modifying them. All are sysfs_dirent renames and trivial. While we can avoid these by introducing a dummy wrapping struct sysfs_dirent around kernfs_node, given the limited usage outside kernfs and sysfs proper, I don't think such workaround is called for. This patch is strictly rename only and doesn't introduce any functional difference. - mic / gpio renames were missing. Spotted by kbuild test robot. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Neil Brown <neilb@suse.de> Cc: Linus Walleij <linus.walleij@linaro.org> Cc: Ashutosh Dixit <ashutosh.dixit@intel.com> Cc: kbuild test robot <fengguang.wu@intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2013-09-27sysfs: clean up sysfs_get_dirent()Tejun Heo1-2/+2
The pre-existing sysfs interfaces which take explicit namespace argument are weird in that they place the optional @ns in front of @name which is contrary to the established convention. For example, we end up forcing vast majority of sysfs_get_dirent() users to do sysfs_get_dirent(parent, NULL, name), which is silly and error-prone especially as @ns and @name may be interchanged without causing compilation warning. This renames sysfs_get_dirent() to sysfs_get_dirent_ns() and swap the positions of @name and @ns, and sysfs_get_dirent() is now a wrapper around sysfs_get_dirent_ns(). This makes confusions a lot less likely. There are other interfaces which take @ns before @name. They'll be updated by following patches. This patch doesn't introduce any functional changes. v2: EXPORT_SYMBOL_GPL() wasn't updated leading to undefined symbol error on module builds. Reported by build test robot. Fixed. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Eric W. Biederman <ebiederm@xmission.com> Cc: Kay Sievers <kay@vrfy.org> Cc: Fengguang Wu <fengguang.wu@intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2013-06-14md: replace strict_strto*() with kstrto*()Jingoo Han1-4/+4
The usage of strict_strtoul() is not preferred, because strict_strtoul() is obsolete. Thus, kstrtoul() should be used. Signed-off-by: Jingoo Han <jg1.han@samsung.com> Signed-off-by: NeilBrown <neilb@suse.de>
2013-04-24md: use set_bit_le and clear_bit_leAkinobu Mita1-2/+2
The value returned by test_and_set_bit_le() drivers/md/bitmap.c is not used. So just use set_bit_le(). The same goes for test_and_clear_bit_le(). Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com> Cc: Neil Brown <neilb@suse.de> Cc: linux-raid@vger.kernel.org Signed-off-by: NeilBrown <neilb@suse.de>
2013-02-23new helper: file_inode(file)Al Viro1-2/+2
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2012-10-11md/bitmap:Don't use IS_ERR to judge alloc_page().Jianpeng Ma1-6/+2
Signed-off-by: Jianpeng Ma <majianpeng@gmail.com> Signed-off-by: NeilBrown <neilb@suse.de>
2012-10-11raid: replace list_for_each_continue_rcu with new interfaceMichael Wang1-6/+3
This patch replaces list_for_each_continue_rcu() with list_for_each_entry_continue_rcu() to save a few lines of code and allow removing list_for_each_continue_rcu(). Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Michael Wang <wangyun@linux.vnet.ibm.com> Signed-off-by: NeilBrown <neilb@suse.de>
2012-08-02md/raid1: submit IO from originating thread instead of md thread.NeilBrown1-1/+1
queuing writes to the md thread means that all requests go through the one processor which may not be able to keep up with very high request rates. So use the plugging infrastructure to submit all requests on unplug. If a 'schedule' is needed, we fall back on the old approach of handing the requests to the thread for it to handle. Signed-off-by: NeilBrown <neilb@suse.de>
2012-05-22md/bitmap: record the space available for the bitmap in the superblock.NeilBrown1-0/+7
Now that bitmaps can grow and shrink it is best if we record how much space is available. This means that when we reduce the size of the bitmap we won't "lose" the space for late when we might want to increase the size of the bitmap again. Signed-off-by: NeilBrown <neilb@suse.de>
2012-05-22md/bitmap: make sure reshape request are reflected in superblock.NeilBrown1-0/+3
As a reshape may change the sync_size and/or chunk_size, we need to update these whenever we write out the bitmap superblock. Signed-off-by: NeilBrown <neilb@suse.de>
2012-05-22md/bitmap: add bitmap_resize function to allow bitmap resizing.NeilBrown1-30/+169
This function will allocate the new data structures and copy bits across from old to new, allowing for the possibility that the chunksize has changed. Use the same function for performing the initial allocation of the structures. This improves test coverage. When bitmap_resize is used to resize an existing bitmap, it only copies '1' bits in, not '0' bits. So when allocating the bitmap, ensure everything is initialised to ZERO. Signed-off-by: NeilBrown <neilb@suse.de>
2012-05-22md/bitmap: use DIV_ROUND_UP instead of open-codeNeilBrown1-3/+2
Also take the opportunity to simplify CHUNK_BLOCK_RATIO. Signed-off-by: NeilBrown <neilb@suse.de>
2012-05-22md/bitmap: create a 'struct bitmap_counts' substructure of 'struct bitmap'NeilBrown1-67/+71
The new "struct bitmap_counts" contains all the fields that are related to counting the number of active writes in each bitmap chunk. Having this separate will make it easier to change the chunksize or overall size of a bitmap atomically. Signed-off-by: NeilBrown <neilb@suse.de>
2012-05-22md/bitmap: make bitmap bitops atomic.NeilBrown1-4/+2
This allows us to remove spinlock protection which is more heavy-weight than simple atomics. Signed-off-by: NeilBrown <neilb@suse.de>
2012-05-22md/bitmap: make _page_attr bitops atomic.NeilBrown1-32/+23
Using e.g. set_bit instead of __set_bit and using test_and_clear_bit allow us to remove some locking and contract other locked ranges. It is rare that we set or clear a lot of these bits, so gain should outweigh any cost. Signed-off-by: NeilBrown <neilb@suse.de>
2012-05-22md/bitmap: merge bitmap_file_unmap and bitmap_file_put.NeilBrown1-24/+10
There functions really do one thing together: release the 'bitmap_storage'. So make them just one function. Since we removed the locking (previous patch), we don't need to zero any fields before freeing them, so it all becomes a bit simpler. Signed-off-by: NeilBrown <neilb@suse.de>
2012-05-22md/bitmap: remove async freeing of bitmap file.NeilBrown1-12/+6
There is no real value in freeing things the moment there is an error. It is just as good to free the bitmap file and pages when the bitmap is explicitly removed (and replaced?) or at shutdown. With this gone, the bitmap will only disappear when the array is quiescent, so we can remove some locking. As the 'filemap' doesn't disappear now, include extra checks before trying to write any of it out. Also remove the check for "has it disappeared" in bitmap_daemon_write(). Signed-off-by: NeilBrown <neilb@suse.de>
2012-05-22md/bitmap: convert some spin_lock_irqsave to spin_lock_irqNeilBrown1-18/+14
All of these sites can only be called from process context with irqs enabled, so using irqsave/irqrestore just adds noise. Remove it. Signed-off-by: NeilBrown <neilb@suse.de>
2012-05-22md/bitmap: use set_bit, test_bit, etc for operation on bitmap->flags.NeilBrown1-25/+21
We currently use '&' and '|' which isn't the norm in the kernel and doesn't allow easy atomicity. So change to bit numbers and {set,clear,test}_bit. This allows us to remove a spinlock/unlock (which was dubious anyway) and some other simplifications. Signed-off-by: NeilBrown <neilb@suse.de>
2012-05-22md/bitmap: remove single-bit manipulation on sb->stateNeilBrown1-2/+2
Just do single-bit manipulations on bitmap->flags and copy whole value between that and sb->state. This will allow next patch which changes how bit manipulations are performed on bitmap->flags. This does result in BITMAP_STALE not being set in sb by bitmap_read_sb, however as the setting is determined by other information in the 'sb' we do not lose information this way. Normally, bitmap_load will be called shortly which will clear BITMAP_STALE anyway. Signed-off-by: NeilBrown <neilb@suse.de>
2012-05-22md/bitmap: remove bitmap_mask_stateNeilBrown1-34/+3
This function isn't really needed. It sets or clears a flag in both bitmap->flags and sb->state. However both times it is called, bitmap_update_sb is called soon afterwards which copies bitmap->flags to sb->state. So just make changes to bitmap->flags, and open-code those rather than hiding in a function. Signed-off-by: NeilBrown <neilb@suse.de>
2012-05-22md/bitmap: move storage allocation from bitmap_load to bitmap_create.NeilBrown1-5/+6
We should allocate memory for the storage-bitmap at create-time, not load time. Signed-off-by: NeilBrown <neilb@suse.de>
2012-05-22md/bitmap: separate bitmap file allocation to its own function.NeilBrown1-46/+67
This will allow allocation before swapping in a new bitmap. Signed-off-by: NeilBrown <neilb@suse.de>
2012-05-22md/bitmap: store bytes in file rather than just in last page.NeilBrown1-7/+9
This number is more generally useful, and bytes-in-last-page is easily extracted from it. Signed-off-by: NeilBrown <neilb@suse.de>