+ readahead-use-ilog2-instead-of-a-while-loop-in-page_cache_ra_order.patch added to mm-unstable branch

+ readahead-use-ilog2-instead-of-a-while-loop-in-page_cache_ra_order.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: readahead: use ilog2 instead of a while loop in page_cache_ra_order()
has been added to the -mm mm-unstable branch.  Its filename is
     readahead-use-ilog2-instead-of-a-while-loop-in-page_cache_ra_order.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/readahead-use-ilog2-instead-of-a-while-loop-in-page_cache_ra_order.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Pankaj Raghav <p.raghav@samsung.com>
Subject: readahead: use ilog2 instead of a while loop in page_cache_ra_order()
Date: Mon, 15 Jan 2024 11:25:22 +0100

A while loop is used to adjust the new_order to be lower than the
ra->size.  ilog2 could be used to do the same instead of using a loop.

ilog2 typically resolves to a bit scan reverse instruction.  This is
particularly useful when ra->size is smaller than the 2^new_order as it
resolves in one instruction instead of looping to find the new_order.

No functional changes.

Link: https://lkml.kernel.org/r/20240115102523.2336742-1-kernel@pankajraghav.com
Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/readahead.c |    6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

--- a/mm/readahead.c~readahead-use-ilog2-instead-of-a-while-loop-in-page_cache_ra_order
+++ a/mm/readahead.c
@@ -500,10 +500,8 @@ void page_cache_ra_order(struct readahea
 
 	if (new_order < MAX_PAGECACHE_ORDER) {
 		new_order += 2;
-		if (new_order > MAX_PAGECACHE_ORDER)
-			new_order = MAX_PAGECACHE_ORDER;
-		while ((1 << new_order) > ra->size)
-			new_order--;
+		new_order = min_t(unsigned int, MAX_PAGECACHE_ORDER, new_order);
+		new_order = min_t(unsigned int, new_order, ilog2(ra->size));
 	}
 
 	filemap_invalidate_lock_shared(mapping);
_

Patches currently in -mm which might be from p.raghav@samsung.com are

readahead-use-ilog2-instead-of-a-while-loop-in-page_cache_ra_order.patch