[PATCH 0/2] Align kvrealloc() with krealloc()

Danilo Krummrich
2024-07-17T22:25:18Z

Hi,

Besides the obvious (and desired) difference between krealloc() and kvrealloc(),
there is some inconsistency in their function signatures and behavior:

- krealloc() frees the memory when the requested size is zero, whereas
kvrealloc() simply returns a pointer to the existing allocation.

- krealloc() behaves like kmalloc() if a NULL pointer is passed, whereas
kvrealloc() does not accept a NULL pointer at all and, if passed, would fault
instead.

- krealloc() is self-contained, whereas kvrealloc() relies on the caller to
provide the size of the previous allocation.

Inconsistent behavior throughout allocation APIs is error prone, hence make
kvrealloc() behave like krealloc(), which seems superior in all mentioned
aspects.

In order to be able to get rid of kvrealloc()'s oldsize parameter, introduce
vrealloc() and make use of it in kvrealloc().

Making use of vrealloc() in kvrealloc() also provides oppertunities to grow (and
shrink) allocations more efficiently. For instance, vrealloc() could be
optimized to extend the existing allocation if there is enough contiguous space
left in the virtual address space at the end of the existing allocation.

Besides the above, those functions are required by Rust's allocator abstractons
[1] (rework based on this series in [2]). With `Vec` or `KVec` respectively,
potentially growing (and shrinking) data structures are rather common.

The patches of this series can also be found in [3].

[1] https://lore.kernel.org/lkml/20240704170738.3621-1-dakr@redhat.com/
[2] https://git.kernel.org/pub/scm/linux/kernel/git/dakr/linux.git/log/?h=rust/mm
[3] https://git.kernel.org/pub/scm/linux/kernel/git/dakr/linux.git/log/?h=mm/krealloc

Danilo Krummrich (2):
mm: vmalloc: implement vrealloc()
mm: kvmalloc: align kvrealloc() with krealloc()

arch/powerpc/platforms/pseries/papr-vpd.c | 5 +-
drivers/gpu/drm/drm_exec.c | 3 +-
fs/xfs/xfs_log_recover.c | 2 +-
include/linux/slab.h | 3 +-
include/linux/vmalloc.h | 4 ++
kernel/resource.c | 3 +-
lib/fortify_kunit.c | 3 +-
mm/util.c | 72 ++++++++++++++++-------
mm/vmalloc.c | 58 ++++++++++++++++++
9 files changed, 118 insertions(+), 35 deletions(-)

base-commit: 51835949dda3783d4639cfa74ce13a3c9829de00
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2.45.2