linux-kernel - Re: [PATCH 3/3] btrfs: Use memzero_page() instead of open coded kmap pattern

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Date:   Fri, 12 Mar 2021 12:23:27 +0100
From:   David Sterba <dsterba@...e.cz>
To:     ira.weiny@...el.com
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        David Sterba <dsterba@...e.com>, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>,
        linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] btrfs: Use memzero_page() instead of open coded kmap
 pattern

On Tue, Mar 09, 2021 at 01:21:37PM -0800, ira.weiny@...el.com wrote:
> From: Ira Weiny <ira.weiny@...el.com>
> 
> There are many places where kmap/memset/kunmap patterns occur.
> 
> Use the newly lifted memzero_page() to eliminate direct uses of kmap and
> leverage the new core functions use of kmap_local_page().
> 
> The development of this patch was aided by the following coccinelle
> script:
> 
> // <smpl>
> // SPDX-License-Identifier: GPL-2.0-only
> // Find kmap/memset/kunmap pattern and replace with memset*page calls
> //
> // NOTE: Offsets and other expressions may be more complex than what the script
> // will automatically generate.  Therefore a catchall rule is provided to find
> // the pattern which then must be evaluated by hand.
> //
> // Confidence: Low
> // Copyright: (C) 2021 Intel Corporation
> // URL: http://coccinelle.lip6.fr/
> // Comments:
> // Options:
> 
> //
> // Then the memset pattern
> //
> @ memset_rule1 @
> expression page, V, L, Off;
> identifier ptr;
> type VP;
> @@
> 
> (
> -VP ptr = kmap(page);
> |
> -ptr = kmap(page);
> |
> -VP ptr = kmap_atomic(page);
> |
> -ptr = kmap_atomic(page);
> )
> <+...
> (
> -memset(ptr, 0, L);
> +memzero_page(page, 0, L);
> |
> -memset(ptr + Off, 0, L);
> +memzero_page(page, Off, L);
> |
> -memset(ptr, V, L);
> +memset_page(page, V, 0, L);
> |
> -memset(ptr + Off, V, L);
> +memset_page(page, V, Off, L);
> )
> ...+>
> (
> -kunmap(page);
> |
> -kunmap_atomic(ptr);
> )
> 
> // Remove any pointers left unused
> @
> depends on memset_rule1
> @
> identifier memset_rule1.ptr;
> type VP, VP1;
> @@
> 
> -VP ptr;
> 	... when != ptr;
> ? VP1 ptr;
> 
> //
> // Catch all
> //
> @ memset_rule2 @
> expression page;
> identifier ptr;
> expression GenTo, GenSize, GenValue;
> type VP;
> @@
> 
> (
> -VP ptr = kmap(page);
> |
> -ptr = kmap(page);
> |
> -VP ptr = kmap_atomic(page);
> |
> -ptr = kmap_atomic(page);
> )
> <+...
> (
> //
> // Some call sites have complex expressions within the memset/memcpy
> // The follow are catch alls which need to be evaluated by hand.
> //
> -memset(GenTo, 0, GenSize);
> +memzero_pageExtra(page, GenTo, GenSize);
> |
> -memset(GenTo, GenValue, GenSize);
> +memset_pageExtra(page, GenValue, GenTo, GenSize);
> )
> ...+>
> (
> -kunmap(page);
> |
> -kunmap_atomic(ptr);
> )
> 
> // Remove any pointers left unused
> @
> depends on memset_rule2
> @
> identifier memset_rule2.ptr;
> type VP, VP1;
> @@
> 
> -VP ptr;
> 	... when != ptr;
> ? VP1 ptr;
> 
> // </smpl>
> 
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>

Reviewed-by: David Sterba <dsterba@...e.com>