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maple tree: add some comments

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Add comments explaining the fields for maple_metadata, since "end" is
ambiguous and "gap" can be confused as the largest gap, whereas it is
actually the offset of the largest gap.

Add comment for mas_ascend() to explain, whose min and max we are trying
to find.  Explain that, for example, if we are already on offset zero,
then the parent min is mas->min, otherwise we need to walk up to find the
implied pivot min.

Link: https://lkml.kernel.org/r/20250703063338.51509-1-dev.jain@arm.com
Signed-off-by: Dev Jain <dev.jain@arm.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Dev Jain 2025-07-03 12:03:38 +05:30 • committed by Andrew Morton
parent 8aa2c0bf0a
commit 526f36f3f4
2 changed files with 9 additions and 3 deletions
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4
include/linux/maple_tree.h
View file

@ -75,8 +75,8 @@
* searching for gaps or any other code that needs to find the end of the data.
*/
struct maple_metadata {
unsigned char end;
unsigned char gap;
unsigned char end; /* end of data */
unsigned char gap; /* offset of largest gap */
};
/*

8
lib/maple_tree.c
View file

@ -1053,7 +1053,7 @@ static inline void mte_set_gap(const struct maple_enode *mn,
* mas_ascend() - Walk up a level of the tree.
* @mas: The maple state
*
* Sets the @mas->max and @mas->min to the correct values when walking up. This
* Sets the @mas->max and @mas->min for the parent node of mas->node. This
* may cause several levels of walking up to find the correct min and max.
* May find a dead node which will cause a premature return.
* Return: 1 on dead node, 0 otherwise
@ -1098,6 +1098,12 @@ static int mas_ascend(struct ma_state *mas)
min = 0;
max = ULONG_MAX;
/*
* !mas->offset implies that parent node min == mas->min.
* mas->offset > 0 implies that we need to walk up to find the
* implied pivot min.
*/
if (!mas->offset) {
min = mas->min;
set_min = true;