linux-kernel - Re: [PATCH] mm/vmalloc: Separate put pages and flush VM flags

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Message-ID: <20210121131932.GO2260413@casper.infradead.org>
Date:   Thu, 21 Jan 2021 13:19:32 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Rick Edgecombe <rick.p.edgecombe@...el.com>
Cc:     akpm@...ux-foundation.org, hch@....de, dja@...ens.net,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/vmalloc: Separate put pages and flush VM flags

On Wed, Jan 20, 2021 at 05:41:18PM -0800, Rick Edgecombe wrote:
> When VM_MAP_PUT_PAGES was added, it was defined with the same value as
> VM_FLUSH_RESET_PERMS. This doesn't seem like it will cause any big
> functional problems other than some excess flushing for VM_MAP_PUT_PAGES
> allocations.
> 
> Redefine VM_MAP_PUT_PAGES to have its own value. Also, move the comment
> and remove whitespace for VM_KASAN such that the flags lower down are less
> likely to be missed in the future.

Er ... I think the problem was that VM_FLUSH_RESET_PERMS was put away from
all the other flags!

Why not this?

diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
index 938eaf9517e26..458c41b99215e 100644
--- a/include/linux/vmalloc.h
+++ b/include/linux/vmalloc.h
@@ -24,7 +24,8 @@ struct notifier_block;		/* in notifier.h */
 #define VM_UNINITIALIZED	0x00000020	/* vm_struct is not fully initialized */
 #define VM_NO_GUARD		0x00000040      /* don't add guard page */
 #define VM_KASAN		0x00000080      /* has allocated kasan shadow memory */
-#define VM_MAP_PUT_PAGES	0x00000100	/* put pages and free array in vfree */
+#define VM_FLUSH_RESET_PERMS	0x00000100      /* Reset direct map and flush TLB on unmap. cannot be freed in atomic context */
+#define VM_MAP_PUT_PAGES	0x00000200	/* put pages and free array in vfree */
 
 /*
  * VM_KASAN is used slighly differently depending on CONFIG_KASAN_VMALLOC.
@@ -37,12 +38,6 @@ struct notifier_block;		/* in notifier.h */
  * determine which allocations need the module shadow freed.
  */
 
-/*
- * Memory with VM_FLUSH_RESET_PERMS cannot be freed in an interrupt or with
- * vfree_atomic().
- */
-#define VM_FLUSH_RESET_PERMS	0x00000100      /* Reset direct map and flush TLB on unmap */
-
 /* bits [20..32] reserved for arch specific ioremap internals */
 
 /*