mm: vmalloc: implement vrealloc()

Patch series "Align kvrealloc() with krealloc()", v2.

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()
can be optimized to allocate and map additional pages to grow the
allocation or unmap and free unused pages to shrink the 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.

[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

This patch (of 2):

Implement vrealloc() analogous to krealloc().

Currently, krealloc() requires the caller to pass the size of the previous
memory allocation, which, instead, should be self-contained.

We attempt to fix this in a subsequent patch which, in order to do so,
requires vrealloc().

Besides that, we need realloc() functions for kernel allocators in Rust
too.  With `Vec` or `KVec` respectively, potentially growing (and
shrinking) data structures are rather common.

Link: https://lkml.kernel.org/r/20240722163111.4766-1-dakr@kernel.org
Link: https://lkml.kernel.org/r/20240722163111.4766-2-dakr@kernel.org
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Chandan Babu R <chandan.babu@oracle.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Kees Cook <kees@kernel.org>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Miguel Ojeda <ojeda@kernel.org>
Cc: Oliver Upton <oliver.upton@linux.dev>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Uladzislau Rezki <urezki@gmail.com>
Cc: Wedson Almeida Filho <wedsonaf@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
index e4a631ec430bb73e764b192a32225b5c7e369245..ad2ce7a6ab7af1d0417af2a427397e191d2af03b 100644 (file)
--- a/include/linux/vmalloc.h
+++ b/include/linux/vmalloc.h
@@ -189,6 +189,10 @@ extern void *__vcalloc_noprof(size_t n, size_t size, gfp_t flags) __alloc_size(1
 extern void *vcalloc_noprof(size_t n, size_t size) __alloc_size(1, 2);
 #define vcalloc(...)           alloc_hooks(vcalloc_noprof(__VA_ARGS__))
 
+void * __must_check vrealloc_noprof(const void *p, size_t size, gfp_t flags)
+               __realloc_size(2);
+#define vrealloc(...)          alloc_hooks(vrealloc_noprof(__VA_ARGS__))
+
 extern void vfree(const void *addr);
 extern void vfree_atomic(const void *addr);
 

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index ac53d46ac8a5c33dea08e38ee3bc5f554dcd0b05..371a84583d7fa27011483874e2daf94ed4cfbcca 100644 (file)
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -4030,6 +4030,65 @@ void *vzalloc_node_noprof(unsigned long size, int node)
 }
 EXPORT_SYMBOL(vzalloc_node_noprof);
 
+/**
+ * vrealloc - reallocate virtually contiguous memory; contents remain unchanged
+ * @p: object to reallocate memory for
+ * @size: the size to reallocate
+ * @flags: the flags for the page level allocator
+ *
+ * The contents of the object pointed to are preserved up to the lesser of the
+ * new and old size (__GFP_ZERO flag is effectively ignored).
+ *
+ * If @p is %NULL, vrealloc() behaves exactly like vmalloc(). If @size is 0 and
+ * @p is not a %NULL pointer, the object pointed to is freed.
+ *
+ * Return: pointer to the allocated memory; %NULL if @size is zero or in case of
+ *         failure
+ */
+void *vrealloc_noprof(const void *p, size_t size, gfp_t flags)
+{
+       size_t old_size = 0;
+       void *n;
+
+       if (!size) {
+               vfree(p);
+               return NULL;
+       }
+
+       if (p) {
+               struct vm_struct *vm;
+
+               vm = find_vm_area(p);
+               if (unlikely(!vm)) {
+                       WARN(1, "Trying to vrealloc() nonexistent vm area (%p)\n", p);
+                       return NULL;
+               }
+
+               old_size = get_vm_area_size(vm);
+       }
+
+       if (size <= old_size) {
+               /*
+                * TODO: Shrink the vm_area, i.e. unmap and free unused pages.
+                * What would be a good heuristic for when to shrink the
+                * vm_area?
+                */
+               return (void *)p;
+       }
+
+       /* TODO: Grow the vm_area, i.e. allocate and map additional pages. */
+       n = __vmalloc_noprof(size, flags);
+       if (!n)
+               return NULL;
+
+       if (p) {
+               memcpy(n, p, old_size);
+               vfree(p);
+       }
+
+       return n;
+}
+
 #if defined(CONFIG_64BIT) && defined(CONFIG_ZONE_DMA32)
 #define GFP_VMALLOC32 (GFP_DMA32 | GFP_KERNEL)
 #elif defined(CONFIG_64BIT) && defined(CONFIG_ZONE_DMA)