GitHub-Mirror/Star64_linux
2
0
Fork 0
mirror of https://github.com/Fishwaldo/Star64_linux.git synced 2025-06-22 22:51:37 +00:00
Code Issues Projects Releases Packages Wiki Activity Actions

XArray: Add support for 1s-based allocation

Browse source 
A lot of places want to allocate IDs starting at 1 instead of 0.
While the xa_alloc() API supports this, it's not very efficient if lots
of IDs are allocated, due to having to walk down to the bottom of the
tree to see if ID 1 is available, then all the way over to the next
non-allocated ID.  This method marks ID 0 as being occupied which wastes
one slot in the XArray, but preserves xa_empty() as working.

Signed-off-by: Matthew Wilcox <willy@infradead.org>
This commit is contained in:
Matthew Wilcox 2018-10-26 14:43:22 -04:00
parent fd9dc93e36
commit 3ccaf57a6a
4 changed files with 86 additions and 37 deletions
Download patch file Download diff file Expand all files Collapse all files

10
Documentation/core-api/xarray.rst
View file

@ -131,17 +131,21 @@ If you use :c:func:`DEFINE_XARRAY_ALLOC` to define the XArray, or
initialise it by passing ``XA_FLAGS_ALLOC`` to :c:func:`xa_init_flags`,
the XArray changes to track whether entries are in use or not.
You can call :c:func:`xa_alloc` to store the entry at any unused index
You can call :c:func:`xa_alloc` to store the entry at an unused index
in the XArray. If you need to modify the array from interrupt context,
you can use :c:func:`xa_alloc_bh` or :c:func:`xa_alloc_irq` to disable
interrupts while allocating the ID.
Using :c:func:`xa_store`, :c:func:`xa_cmpxchg` or :c:func:`xa_insert`
will mark the entry as being allocated. Unlike a normal XArray, storing
Using :c:func:`xa_store`, :c:func:`xa_cmpxchg` or :c:func:`xa_insert` will
also mark the entry as being allocated. Unlike a normal XArray, storing
``NULL`` will mark the entry as being in use, like :c:func:`xa_reserve`.
To free an entry, use :c:func:`xa_erase` (or :c:func:`xa_release` if
you only want to free the entry if it's ``NULL``).
By default, the lowest free entry is allocated starting from 0. If you
want to allocate entries starting at 1, it is more efficient to use
:c:func:`DEFINE_XARRAY_ALLOC1` or ``XA_FLAGS_ALLOC1``.
You cannot use ``XA_MARK_0`` with an allocating XArray as this mark
is used to track whether an entry is free or not. The other marks are
available for your use.