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md/bitmap tracks how many active write requests are pending on blocks
associated with each bit in the bitmap, so that it knows when it can clear
the bit (when count hits zero).
The counter has 14 bits of space, so if there are ever more than 16383, we
cannot cope.
Currently the code just calles BUG_ON as "all" drivers have request queue
limits much smaller than this.
However is seems that some don't. Apparently some multipath configurations
can allow more than 16383 concurrent write requests.
So, in this unlikely situation, instead of calling BUG_ON we now wait
for the count to drop down a bit. This requires a new wait_queue_head,
some waiting code, and a wakeup call.
Tested by limiting the counter to 20 instead of 16383 (writes go a lot slower
in that case...).
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Adrian Bunk <bunk@kernel.org>
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bitmap_active is never called, and the BITMAP_ACTIVE flag is never users or
tested, so discard them both.
Also remove some out-of-date 'todo' comments.
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Adrian Bunk <bunk@kernel.org>
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Current bitmaps use set_bit et.al and so are host-endian, which means
not-portable. Oops.
Define a new version number (4) for which bitmaps are little-endian.
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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If a device is flagged 'WriteMostly' and the array has a bitmap, and the
bitmap superblock indicates that write_behind is allowed, then write_behind is
enabled for WriteMostly devices.
Write requests will be acknowledges as complete to the caller (via b_end_io)
when all non-WriteMostly devices have completed the write, but will not be
cleared from the bitmap until all devices complete.
This requires memory allocation to make a local copy of the data being
written. If there is insufficient memory, then we fall-back on normal write
semantics.
Signed-Off-By: Paul Clements <paul.clements@steeleye.com>
Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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The recent change to never ignore the bitmap, revealed that the bitmap isn't
begin flushed properly when an array is stopped.
We call bitmap_daemon_work three times as there is a three-stage pipeline for
flushing updates to the bitmap file.
Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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We need to be careful differentiating between a resync of a complete array,
in which we can clear the bitmap, and a resync of a degraded array, in
which we cannot.
This patch cleans all that up.
Cc: Paul Clements <paul.clements@steeleye.com>
Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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This provides an alternate to storing the bitmap in a separate file. The
bitmap can be stored at a given offset from the superblock. Obviously the
creator of the array must make sure this doesn't intersect with data....
After is good for version-0.90 superblocks.
Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Currently we don't wait for updates to the bitmap to be flushed to disk
properly. The infrastructure all there, but it isn't being used....
A separate kernel thread (bitmap_writeback_daemon) is needed to wait for each
page as we cannot get callbacks when a page write completes.
Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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With this patch, the intent to write to some block in the array can be logged
to a bitmap file. Each bit represents some number of sectors and is set
before any update happens, and only cleared when all writes relating to all
sectors are complete.
After an unclean shutdown, information in this bitmap can be used to optimise
resync - only sectors which could be out-of-sync need to be updated.
Also if a drive is removed and then added back into an array, the recovery can
make use of the bitmap to optimise reconstruction. This is not implemented in
this patch.
Currently the bitmap is stored in a file which must (obviously) be stored on a
separate device.
The patch only provided infrastructure. It does not update any personalities
to bitmap intent logging.
Md arrays can still be used with no bitmap file. This patch has minimal
impact on such arrays.
Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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