linux-kernel - [PATCH] gfp: further document GFP

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Message-ID: <20211207093610.6406-1-miles.chen@mediatek.com>
Date:   Tue, 7 Dec 2021 17:36:10 +0800
From:   Miles Chen <miles.chen@...iatek.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
CC:     <linux-kernel@...r.kernel.org>,
        <linux-mediatek@...ts.infradead.org>, <wsd_upstream@...iatek.com>,
        Miles Chen <miles.chen@...iatek.com>
Subject: [PATCH] gfp: 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

Signed-off-by: Miles Chen <miles.chen@...iatek.com>
---
 include/linux/gfp.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index b976c4177299..c7bfaa9f3903 100644
--- 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
-- 
2.18.0