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dax: remove the pmem_dax_ops->flush abstraction

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Commit abebfbe2f7 ("dm: add ->flush() dax operation support") is
buggy. A DM device may be composed of multiple underlying devices and
all of them need to be flushed. That commit just routes the flush
request to the first device and ignores the other devices.

It could be fixed by adding more complex logic to the device mapper. But
there is only one implementation of the method pmem_dax_ops->flush - that
is pmem_dax_flush() - and it calls arch_wb_cache_pmem(). Consequently, we
don't need the pmem_dax_ops->flush abstraction at all, we can call
arch_wb_cache_pmem() directly from dax_flush() because dax_dev->ops->flush
can't ever reach anything different from arch_wb_cache_pmem().

It should be also pointed out that for some uses of persistent memory it
is needed to flush only a very small amount of data (such as 1 cacheline),
and it would be overkill if we go through that device mapper machinery for
a single flushed cache line.

Fix this by removing the pmem_dax_ops->flush abstraction and call
arch_wb_cache_pmem() directly from dax_flush(). Also, remove the device
mapper code that forwards the flushes.

Fixes: abebfbe2f7 ("dm: add ->flush() dax operation support")
Cc: [email protected]
Signed-off-by: Mikulas Patocka <[email protected]>
Reviewed-by: Dan Williams <[email protected]>
Signed-off-by: Mike Snitzer <[email protected]>
This commit is contained in:
Mikulas Patocka 2017-08-31 21:47:43 -04:00 • committed by Mike Snitzer
commit c3ca015fab
8 changed files with 17 additions and 77 deletions
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7
drivers/nvdimm/pmem.c
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@ -243,16 +243,9 @@ static size_t pmem_copy_from_iter(struct dax_device *dax_dev, pgoff_t pgoff,
return copy_from_iter_flushcache(addr, bytes, i);
}
static void pmem_dax_flush(struct dax_device *dax_dev, pgoff_t pgoff,
void *addr, size_t size)
{
arch_wb_cache_pmem(addr, size);
}
static const struct dax_operations pmem_dax_ops = {
.direct_access = pmem_dax_direct_access,
.copy_from_iter = pmem_copy_from_iter,
.flush = pmem_dax_flush,
};
static const struct attribute_group *pmem_attribute_groups[] = {