On Thu 28-02-19 20:24:48, Matthew Wilcox wrote:
> The radix tree would rewind the index in an iterator to the lowest index
> of a multi-slot entry. The XArray iterators instead leave the index
> unchanged, but I overlooked that when converting DAX from the radix tree
> to the XArray. Adjust the index that we use for flushing to the start
> of the PMD range.
>
> Fixes: c1901cd33cf4 "page cache: Convert find_get_entries_tag to XArray"
> Reported-by: Piotr Balcer <[email protected]>
> Tested-by: Dan Williams <[email protected]>
> Signed-off-by: Matthew Wilcox <[email protected]>
> ---
Thanks for the patch! One comment below:
> @@ -894,17 +893,18 @@ static int dax_writeback_one(struct xa_state *xas,
> struct dax_device *dax_dev,
> xas_unlock_irq(xas);
>
> /*
> - * Even if dax_writeback_mapping_range() was given a wbc->range_start
> - * in the middle of a PMD, the 'index' we are given will be aligned to
> - * the start index of the PMD, as will the pfn we pull from 'entry'.
> + * If dax_writeback_mapping_range() was given a wbc->range_start
> + * in the middle of a PMD, the 'index' we are given needs to be
> + * aligned to the start index of the PMD.
> * This allows us to flush for PMD_SIZE and not have to worry about
> * partial PMD writebacks.
> */
> pfn = dax_to_pfn(entry);
> - size = PAGE_SIZE << dax_entry_order(entry);
> + count = 1UL << dax_entry_order(entry);
> + index = xas->xa_index &~ (count - 1);
Hum, why do you compute 'index' here when you actually never use it? The
whole patch looks fishy since it is effectively a noop AFAICT...
Honza
>
> dax_entry_mkclean(mapping, xas->xa_index, pfn);
> - dax_flush(dax_dev, page_address(pfn_to_page(pfn)), size);
> + dax_flush(dax_dev, page_address(pfn_to_page(pfn)), count * PAGE_SIZE);
> /*
> * After we have flushed the cache, we can clear the dirty tag. There
> * cannot be new dirty data in the pfn after the flush has completed as
> @@ -917,8 +917,7 @@ static int dax_writeback_one(struct xa_state *xas, struct
> dax_device *dax_dev,
> xas_clear_mark(xas, PAGECACHE_TAG_DIRTY);
> dax_wake_entry(xas, entry, false);
>
> - trace_dax_writeback_one(mapping->host, xas->xa_index,
> - size >> PAGE_SHIFT);
> + trace_dax_writeback_one(mapping->host, xas->xa_index, count);
> return ret;
>
> put_unlocked:
> --
> 2.20.1
>
--
Jan Kara <[email protected]>
SUSE Labs, CR
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