linux-kernel - [PATCH] mm/vmalloc: be more explicit about supported gfp flags.

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Message-Id: <20211020082545.4830-1-mhocko@kernel.org>
Date:   Wed, 20 Oct 2021 10:25:45 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     <linux-mm@...ck.org>
Cc:     Dave Chinner <david@...morbit.com>, Neil Brown <neilb@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Hellwig <hch@...radead.org>,
        Uladzislau Rezki <urezki@...il.com>,
        <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ilya Dryomov <idryomov@...il.com>,
        Jeff Layton <jlayton@...nel.org>,
        Michal Hocko <mhocko@...e.com>
Subject: [PATCH] mm/vmalloc: be more explicit about supported gfp flags.

From: Michal Hocko <mhocko@...e.com>

The core of the vmalloc allocator __vmalloc_area_node doesn't say
anything about gfp mask argument. Not all gfp flags are supported
though. Be more explicit about constrains.

Signed-off-by: Michal Hocko <mhocko@...e.com>
---
 mm/vmalloc.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index f7098e616883..f57c09e98977 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2979,8 +2979,16 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
  * @caller:		  caller's return address
  *
  * Allocate enough pages to cover @size from the page level
- * allocator with @gfp_mask flags.  Map them into contiguous
- * kernel virtual space, using a pagetable protection of @prot.
+ * allocator with @gfp_mask flags. Please note that the full set of gfp
+ * flags are not supported. GFP_KERNEL would be a preferred allocation mode
+ * but GFP_NOFS and GFP_NOIO are supported as well. Zone modifiers are not
+ * supported. From the reclaim modifiers__GFP_DIRECT_RECLAIM is required (aka
+ * GFP_NOWAIT is not supported) and only __GFP_NOFAIL is supported (aka
+ * __GFP_NORETRY and __GFP_RETRY_MAYFAIL are not supported).
+ * __GFP_NOWARN can be used to suppress error messages about failures.
+ * 
+ * Map them into contiguous kernel virtual space, using a pagetable
+ * protection of @prot.
  *
  * Return: the address of the area or %NULL on failure
  */
-- 
2.30.2