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mm: Use multi-index entries in the page cache

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We currently store large folios as 2^N consecutive entries.  While this
consumes rather more memory than necessary, it also turns out to be buggy.
A writeback operation which starts within a tail page of a dirty folio will
not write back the folio as the xarray's dirty bit is only set on the
head index.  With multi-index entries, the dirty bit will be found no
matter where in the folio the operation starts.

This does end up simplifying the page cache slightly, although not as
much as I had hoped.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
This commit is contained in:
Matthew Wilcox (Oracle) 2020-06-27 22:19:08 -04:00
parent 25a8de7f8d
commit 6b24ca4a1a
6 changed files with 72 additions and 56 deletions
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10
include/linux/pagemap.h
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@ -1125,16 +1125,6 @@ static inline unsigned int __readahead_batch(struct readahead_control *rac,
VM_BUG_ON_PAGE(PageTail(page), page);
array[i++] = page;
rac->_batch_count += thp_nr_pages(page);
/*
* The page cache isn't using multi-index entries yet,
* so the xas cursor needs to be manually moved to the
* next index. This can be removed once the page cache
* is converted.
*/
if (PageHead(page))
xas_set(&xas, rac->_index + rac->_batch_count);
if (i == array_sz)
break;
}