include/linux/gfp.h: further document GFP_DMA32

kmalloc(..., GFP_DMA32) does not return DMA32 memory because the DMA32 kmalloc cache array is not implemented. (Reason: there is no such user in kernel). Put a short comment about this so people can understand this by reading the comment. [1] https://lists.linuxfoundation.org/pipermail/iommu/2018-December/031696.html Link: https://lkml.kernel.org/r/[email protected] Signed-off-by: Miles Chen <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
wafgo · Jan 15, 2022 · 04a536b · 04a536b
1 parent be1a13e
commit 04a536b
Showing 1 changed file with 3 additions and 1 deletion.
diff --git a/include/linux/gfp.h b/include/linux/gfp.h
@@ -302,7 +302,9 @@ struct vm_area_struct;
  * lowest zone as a type of emergency reserve.
  *
  * %GFP_DMA32 is similar to %GFP_DMA except that the caller requires a 32-bit
- * address.
+ * address. Note that kmalloc(..., GFP_DMA32) does not return DMA32 memory
+ * because the DMA32 kmalloc cache array is not implemented.
+ * (Reason: there is no such user in kernel).
  *
  * %GFP_HIGHUSER is for userspace allocations that may be mapped to userspace,
  * do not need to be directly accessible by the kernel but that cannot