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xarray: Add xa_reserve and xa_release

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This function reserves a slot in the XArray for users which need
to acquire multiple locks before storing their entry in the tree and
so cannot use a plain xa_store().

Signed-off-by: Matthew Wilcox <willy@infradead.org>
This commit is contained in:
Matthew Wilcox
2018-10-01 14:54:59 -04:00
parent 2264f5132f
commit 9f14d4f1f1
4 changed files with 125 additions and 2 deletions
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34
include/linux/xarray.h
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@@ -32,7 +32,8 @@
* The following internal entries have a special meaning:
*
* 0-62: Sibling entries
* 256: Retry entry
* 256: Zero entry
* 257: Retry entry
*
* Errors are also represented as internal entries, but use the negative
* space (-4094 to -2). They're never stored in the slots array; only
@@ -277,6 +278,7 @@ void *xa_load(struct xarray *, unsigned long index);
void *xa_store(struct xarray *, unsigned long index, void *entry, gfp_t);
void *xa_cmpxchg(struct xarray *, unsigned long index,
void *old, void *entry, gfp_t);
int xa_reserve(struct xarray *, unsigned long index, gfp_t);
bool xa_get_mark(struct xarray *, unsigned long index, xa_mark_t);
void xa_set_mark(struct xarray *, unsigned long index, xa_mark_t);
void xa_clear_mark(struct xarray *, unsigned long index, xa_mark_t);
@@ -371,6 +373,20 @@ static inline int xa_insert(struct xarray *xa, unsigned long index,
return -EEXIST;
}
/**
* xa_release() - Release a reserved entry.
* @xa: XArray.
* @index: Index of entry.
*
* After calling xa_reserve(), you can call this function to release the
* reservation. If the entry at @index has been stored to, this function
* will do nothing.
*/
static inline void xa_release(struct xarray *xa, unsigned long index)
{
xa_cmpxchg(xa, index, NULL, NULL, 0);
}
/**
* xa_for_each() - Iterate over a portion of an XArray.
* @xa: XArray.
@@ -658,7 +674,19 @@ static inline bool xa_is_sibling(const void *entry)
(entry < xa_mk_sibling(XA_CHUNK_SIZE - 1));
}
#define XA_RETRY_ENTRY xa_mk_internal(256)
#define XA_ZERO_ENTRY xa_mk_internal(256)
#define XA_RETRY_ENTRY xa_mk_internal(257)
/**
* xa_is_zero() - Is the entry a zero entry?
* @entry: Entry retrieved from the XArray
*
* Return: %true if the entry is a zero entry.
*/
static inline bool xa_is_zero(const void *entry)
{
return unlikely(entry == XA_ZERO_ENTRY);
}
/**
* xa_is_retry() - Is the entry a retry entry?
@@ -880,6 +908,8 @@ static inline void xas_reset(struct xa_state *xas)
*/
static inline bool xas_retry(struct xa_state *xas, const void *entry)
{
if (xa_is_zero(entry))
return true;
if (!xa_is_retry(entry))
return false;
xas_reset(xas);