Patch "alloc_tag: avoid current->alloc_tag manipulations when profiling is disabled" has been added to the 6.13-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    alloc_tag: avoid current->alloc_tag manipulations when profiling is disabled

to the 6.13-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:
     alloc_tag-avoid-current-alloc_tag-manipulations-when.patch
and it can be found in the queue-6.13 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 8c053d96ade6de95015849ac65dd5d13a66bc2fd
Author: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Date:   Thu Dec 26 13:16:38 2024 -0800

    alloc_tag: avoid current->alloc_tag manipulations when profiling is disabled
    
    [ Upstream commit 07438779313caafe52ac1a1a6958d735a5938988 ]
    
    When memory allocation profiling is disabled there is no need to update
    current->alloc_tag and these manipulations add unnecessary overhead.  Fix
    the overhead by skipping these extra updates.
    
    I ran comprehensive testing on Pixel 6 on Big, Medium and Little cores:
    
                     Overhead before fixes            Overhead after fixes
                     slab alloc      page alloc          slab alloc      page alloc
    Big               6.21%           5.32%                3.31%          4.93%
    Medium            4.51%           5.05%                3.79%          4.39%
    Little            7.62%           1.82%                6.68%          1.02%
    
    This is an allocation microbenchmark doing allocations in a tight loop.
    Not a really realistic scenario and useful only to make performance
    comparisons.
    
    Link: https://lkml.kernel.org/r/20241226211639.1357704-1-surenb@xxxxxxxxxx
    Fixes: b951aaff5035 ("mm: enable page allocation tagging")
    Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
    Cc: David Wang <00107082@xxxxxxx>
    Cc: Kent Overstreet <kent.overstreet@xxxxxxxxx>
    Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
    Cc: Zhenhua Huang <quic_zhenhuah@xxxxxxxxxxx>
    Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/include/linux/alloc_tag.h b/include/linux/alloc_tag.h
index 0bbbe537c5f9f..a946e0203e6d6 100644
--- a/include/linux/alloc_tag.h
+++ b/include/linux/alloc_tag.h
@@ -224,9 +224,14 @@ static inline void alloc_tag_sub(union codetag_ref *ref, size_t bytes) {}
 
 #define alloc_hooks_tag(_tag, _do_alloc)				\
 ({									\
-	struct alloc_tag * __maybe_unused _old = alloc_tag_save(_tag);	\
-	typeof(_do_alloc) _res = _do_alloc;				\
-	alloc_tag_restore(_tag, _old);					\
+	typeof(_do_alloc) _res;						\
+	if (mem_alloc_profiling_enabled()) {				\
+		struct alloc_tag * __maybe_unused _old;			\
+		_old = alloc_tag_save(_tag);				\
+		_res = _do_alloc;					\
+		alloc_tag_restore(_tag, _old);				\
+	} else								\
+		_res = _do_alloc;					\
 	_res;								\
 })
 
diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c
index 65e706e1bc199..4e5d7af3eaa22 100644
--- a/lib/alloc_tag.c
+++ b/lib/alloc_tag.c
@@ -29,6 +29,8 @@ EXPORT_SYMBOL(_shared_alloc_tag);
 
 DEFINE_STATIC_KEY_MAYBE(CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT,
 			mem_alloc_profiling_key);
+EXPORT_SYMBOL(mem_alloc_profiling_key);
+
 DEFINE_STATIC_KEY_FALSE(mem_profiling_compressed);
 
 struct alloc_tag_kernel_section kernel_tags = { NULL, 0 };