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XArray: add xas_split

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In order to use multi-index entries for huge pages in the page cache, we
need to be able to split a multi-index entry (eg if a file is truncated in
the middle of a huge page entry).  This version does not support splitting
more than one level of the tree at a time.  This is an acceptable
limitation for the page cache as we do not expect to support order-12
pages in the near future.

[akpm@linux-foundation.org: export xas_split_alloc() to modules]
[willy@infradead.org: fix xarray split]
  Link: https://lkml.kernel.org/r/20200910175450.GV6583@casper.infradead.org
[willy@infradead.org: fix xarray]
  Link: https://lkml.kernel.org/r/20201001233943.GW20115@casper.infradead.org

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: "Kirill A . Shutemov" <kirill@shutemov.name>
Cc: Qian Cai <cai@lca.pw>
Cc: Song Liu <songliubraving@fb.com>
Link: https://lkml.kernel.org/r/20200903183029.14930-3-willy@infradead.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Matthew Wilcox (Oracle)
2020-10-15 20:05:16 -07:00
committed by Linus Torvalds
parent 57417cebc9
commit 8fc75643c5
4 changed files with 224 additions and 15 deletions
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14
Documentation/core-api/xarray.rst
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@@ -475,13 +475,15 @@ or iterations will move the index to the first index in the range.
Each entry will only be returned once, no matter how many indices it
occupies.
Using xas_next() or xas_prev() with a multi-index xa_state
is not supported. Using either of these functions on a multi-index entry
will reveal sibling entries; these should be skipped over by the caller.
Using xas_next() or xas_prev() with a multi-index xa_state is not
supported. Using either of these functions on a multi-index entry will
reveal sibling entries; these should be skipped over by the caller.
Storing ``NULL`` into any index of a multi-index entry will set the entry
at every index to ``NULL`` and dissolve the tie. Splitting a multi-index
entry into entries occupying smaller ranges is not yet supported.
Storing ``NULL`` into any index of a multi-index entry will set the
entry at every index to ``NULL`` and dissolve the tie. A multi-index
entry can be split into entries occupying smaller ranges by calling
xas_split_alloc() without the xa_lock held, followed by taking the lock
and calling xas_split().
Functions and structures
========================