Patch "minmax: simplify min()/max()/clamp() implementation" has been added to the 5.15-stable tree
gregkh at linuxfoundation.org
gregkh at linuxfoundation.org
Fri Oct 17 01:16:17 PDT 2025
This is a note to let you know that I've just added the patch titled
minmax: simplify min()/max()/clamp() implementation
to the 5.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
minmax-simplify-min-max-clamp-implementation.patch
and it can be found in the queue-5.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable at vger.kernel.org> know about it.
>From prvs=36971892a=farbere at amazon.com Wed Oct 8 17:32:42 2025
From: Eliav Farber <farbere at amazon.com>
Date: Wed, 8 Oct 2025 15:29:35 +0000
Subject: minmax: simplify min()/max()/clamp() implementation
To: <gregkh at linuxfoundation.org>, <jdike at addtoit.com>, <richard at nod.at>, <anton.ivanov at cambridgegreys.com>, <dave.hansen at linux.intel.com>, <luto at kernel.org>, <peterz at infradead.org>, <tglx at linutronix.de>, <mingo at redhat.com>, <bp at alien8.de>, <x86 at kernel.org>, <hpa at zytor.com>, <tony.luck at intel.com>, <qiuxu.zhuo at intel.com>, <james.morse at arm.com>, <rric at kernel.org>, <airlied at linux.ie>, <daniel at ffwll.ch>, <maarten.lankhorst at linux.intel.com>, <mripard at kernel.org>, <tzimmermann at suse.de>, <robdclark at gmail.com>, <sean at poorly.run>, <jdelvare at suse.com>, <linux at roeck-us.net>, <linus.walleij at linaro.org>, <dmitry.torokhov at gmail.com>, <maz at kernel.org>, <wens at csie.org>, <jernej.skrabec at gmail.com>, <agk at redhat.com>, <snitzer at redhat.com>, <dm-devel at redhat.com>, <davem at davemloft.net>, <kuba at kernel.org>, <mcoquelin.stm32 at gmail.com>, <krzysztof.kozlowski at canonical.com>, <malattia at linux.it>, <hdegoede at redhat.com>, <mgross at linux.intel.com>, <jejb at linux.ibm.com>, <martin.petersen at oracle.com>, <sakari.ailus at l
inux.intel.com>, <clm at fb.com>, <josef at toxicpanda.com>, <dsterba at suse.com>, <jack at suse.com>, <tytso at mit.edu>, <adilger.kernel at dilger.ca>, <dushistov at mail.ru>, <luc.vanoostenryck at gmail.com>, <rostedt at goodmis.org>, <pmladek at suse.com>, <senozhatsky at chromium.org>, <andriy.shevchenko at linux.intel.com>, <linux at rasmusvillemoes.dk>, <minchan at kernel.org>, <ngupta at vflare.org>, <akpm at linux-foundation.org>, <yoshfuji at linux-ipv6.org>, <dsahern at kernel.org>, <pablo at netfilter.org>, <kadlec at netfilter.org>, <fw at strlen.de>, <jmaloy at redhat.com>, <ying.xue at windriver.com>, <shuah at kernel.org>, <willy at infradead.org>, <farbere at amazon.com>, <sashal at kernel.org>, <quic_akhilpo at quicinc.com>, <ruanjinjie at huawei.com>, <David.Laight at ACULAB.COM>, <herve.codina at bootlin.com>, <linux-arm-kernel at lists.infradead.org>, <linux-kernel at vger.kernel.org>, <linux-um at lists.infradead.org>, <linux-edac at vger.kernel.org>, <amd-gfx at lists.freedesktop.org>, <dri-devel at lists.freedesktop.org>, <linux-arm-msm at vger.kernel.org>, <freedreno at l
ists.freedesktop.org>, <linux-hwmon at vger.kernel.org>, <linux-input at vger.kernel.org>, <linux-sunxi at lists.linux.dev>, <linux-media at vger.kernel.org>, <netdev at vger.kernel.org>, <linux-stm32 at st-md-mailman.stormreply.com>, <platform-driver-x86 at vger.kernel.org>, <linux-scsi at vger.kernel.org>, <linux-staging at lists.linux.dev>, <linux-btrfs at vger.kernel.org>, <linux-ext4 at vger.kernel.org>, <linux-sparse at vger.kernel.org>, <linux-mm at kvack.org>, <netfilter-devel at vger.kernel.org>, <coreteam at netfilter.org>, <tipc-discussion at lists.sourceforge.net>, <linux-kselftest at vger.kernel.org>, <stable at vger.kernel.org>
Cc: Linus Torvalds <torvalds at linux-foundation.org>, David Laight <David.Laight at aculab.com>, Lorenzo Stoakes <lorenzo.stoakes at oracle.com>
Message-ID: <20251008152946.29285-11-farbere at amazon.com>
From: Linus Torvalds <torvalds at linux-foundation.org>
[ Upstream commit dc1c8034e31b14a2e5e212104ec508aec44ce1b9 ]
Now that we no longer have any C constant expression contexts (ie array
size declarations or static initializers) that use min() or max(), we
can simpify the implementation by not having to worry about the result
staying as a C constant expression.
So now we can unconditionally just use temporary variables of the right
type, and get rid of the excessive expansion that used to come from the
use of
__builtin_choose_expr(__is_constexpr(...), ..
to pick the specialized code for constant expressions.
Another expansion simplification is to pass the temporary variables (in
addition to the original expression) to our __types_ok() macro. That
may superficially look like it complicates the macro, but when we only
want the type of the expression, expanding the temporary variable names
is much simpler and smaller than expanding the potentially complicated
original expression.
As a result, on my machine, doing a
$ time make drivers/staging/media/atomisp/pci/isp/kernels/ynr/ynr_1.0/ia_css_ynr.host.i
goes from
real 0m16.621s
user 0m15.360s
sys 0m1.221s
to
real 0m2.532s
user 0m2.091s
sys 0m0.452s
because the token expansion goes down dramatically.
In particular, the longest line expansion (which was line 71 of that
'ia_css_ynr.host.c' file) shrinks from 23,338kB (yes, 23MB for one
single line) to "just" 1,444kB (now "only" 1.4MB).
And yes, that line is still the line from hell, because it's doing
multiple levels of "min()/max()" expansion thanks to some of them being
hidden inside the uDIGIT_FITTING() macro.
Lorenzo has a nice cleanup patch that makes that driver use inline
functions instead of macros for sDIGIT_FITTING() and uDIGIT_FITTING(),
which will fix that line once and for all, but the 16-fold reduction in
this case does show why we need to simplify these helpers.
Cc: David Laight <David.Laight at aculab.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes at oracle.com>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Eliav Farber <farbere at amazon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
---
include/linux/minmax.h | 43 ++++++++++++++++++++-----------------------
1 file changed, 20 insertions(+), 23 deletions(-)
--- a/include/linux/minmax.h
+++ b/include/linux/minmax.h
@@ -35,10 +35,10 @@
#define __is_noneg_int(x) \
(__builtin_choose_expr(__is_constexpr(x) && __is_signed(x), x, -1) >= 0)
-#define __types_ok(x, y) \
- (__is_signed(x) == __is_signed(y) || \
- __is_signed((x) + 0) == __is_signed((y) + 0) || \
- __is_noneg_int(x) || __is_noneg_int(y))
+#define __types_ok(x, y, ux, uy) \
+ (__is_signed(ux) == __is_signed(uy) || \
+ __is_signed((ux) + 0) == __is_signed((uy) + 0) || \
+ __is_noneg_int(x) || __is_noneg_int(y))
#define __cmp_op_min <
#define __cmp_op_max >
@@ -51,34 +51,31 @@
#define __cmp_once(op, type, x, y) \
__cmp_once_unique(op, type, x, y, __UNIQUE_ID(x_), __UNIQUE_ID(y_))
-#define __careful_cmp_once(op, x, y) ({ \
- static_assert(__types_ok(x, y), \
+#define __careful_cmp_once(op, x, y, ux, uy) ({ \
+ __auto_type ux = (x); __auto_type uy = (y); \
+ static_assert(__types_ok(x, y, ux, uy), \
#op "(" #x ", " #y ") signedness error, fix types or consider u" #op "() before " #op "_t()"); \
- __cmp_once(op, __auto_type, x, y); })
+ __cmp(op, ux, uy); })
-#define __careful_cmp(op, x, y) \
- __builtin_choose_expr(__is_constexpr((x) - (y)), \
- __cmp(op, x, y), __careful_cmp_once(op, x, y))
+#define __careful_cmp(op, x, y) \
+ __careful_cmp_once(op, x, y, __UNIQUE_ID(x_), __UNIQUE_ID(y_))
#define __clamp(val, lo, hi) \
((val) >= (hi) ? (hi) : ((val) <= (lo) ? (lo) : (val)))
-#define __clamp_once(val, lo, hi, unique_val, unique_lo, unique_hi) ({ \
- typeof(val) unique_val = (val); \
- typeof(lo) unique_lo = (lo); \
- typeof(hi) unique_hi = (hi); \
+#define __clamp_once(val, lo, hi, uval, ulo, uhi) ({ \
+ __auto_type uval = (val); \
+ __auto_type ulo = (lo); \
+ __auto_type uhi = (hi); \
static_assert(__builtin_choose_expr(__is_constexpr((lo) > (hi)), \
(lo) <= (hi), true), \
"clamp() low limit " #lo " greater than high limit " #hi); \
- static_assert(__types_ok(val, lo), "clamp() 'lo' signedness error"); \
- static_assert(__types_ok(val, hi), "clamp() 'hi' signedness error"); \
- __clamp(unique_val, unique_lo, unique_hi); })
-
-#define __careful_clamp(val, lo, hi) ({ \
- __builtin_choose_expr(__is_constexpr((val) - (lo) + (hi)), \
- __clamp(val, lo, hi), \
- __clamp_once(val, lo, hi, __UNIQUE_ID(__val), \
- __UNIQUE_ID(__lo), __UNIQUE_ID(__hi))); })
+ static_assert(__types_ok(uval, lo, uval, ulo), "clamp() 'lo' signedness error"); \
+ static_assert(__types_ok(uval, hi, uval, uhi), "clamp() 'hi' signedness error"); \
+ __clamp(uval, ulo, uhi); })
+
+#define __careful_clamp(val, lo, hi) \
+ __clamp_once(val, lo, hi, __UNIQUE_ID(v_), __UNIQUE_ID(l_), __UNIQUE_ID(h_))
/**
* min - return minimum of two values of the same or compatible types
Patches currently in stable-queue which might be from farbere at amazon.com are
queue-5.15/minmax-add-a-few-more-min_t-max_t-users.patch
queue-5.15/minmax-improve-macro-expansion-and-type-checking.patch
queue-5.15/minmax-fix-indentation-of-__cmp_once-and-__clamp_once.patch
queue-5.15/minmax.h-simplify-the-variants-of-clamp.patch
queue-5.15/minmax-add-in_range-macro.patch
queue-5.15/minmax.h-move-all-the-clamp-definitions-after-the-min-max-ones.patch
queue-5.15/minmax-don-t-use-max-in-situations-that-want-a-c-constant-expression.patch
queue-5.15/minmax.h-remove-some-defines-that-are-only-expanded-once.patch
queue-5.15/minmax.h-use-build_bug_on_msg-for-the-lo-hi-test-in-clamp.patch
queue-5.15/minmax-simplify-min-max-clamp-implementation.patch
queue-5.15/minmax-deduplicate-__unconst_integer_typeof.patch
queue-5.15/minmax-simplify-and-clarify-min_t-max_t-implementation.patch
queue-5.15/minmax.h-add-whitespace-around-operators-and-after-commas.patch
queue-5.15/minmax-avoid-overly-complicated-constant-expressions-in-vm-code.patch
queue-5.15/minmax-make-generic-min-and-max-macros-available-everywhere.patch
queue-5.15/minmax-fix-up-min3-and-max3-too.patch
queue-5.15/minmax.h-reduce-the-define-expansion-of-min-max-and-clamp.patch
queue-5.15/minmax-introduce-min-max-_array.patch
queue-5.15/minmax.h-update-some-comments.patch
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