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include/linux/gfp.h: further document GFP_DMA32

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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/20211207093610.6406-1-miles.chen@mediatek.com
Signed-off-by: Miles Chen <miles.chen@mediatek.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Miles Chen 2022-01-14 14:07:30 -08:00 committed by Linus Torvalds
parent be1a13eb51
commit 04a536bfbd
1 changed files with 3 additions and 1 deletions
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4
include/linux/gfp.h
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@ -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