Commit 9cd28575 authored by Pankaj Raghav's avatar Pankaj Raghav Committed by Liu Shixin
Browse files

readahead: use ilog2 instead of a while loop in page_cache_ra_order() 

mainline inclusion
from mainline-v6.9-rc1
commit e03c16fb4af1dfc615a4e1f51be0d5fe5840b904
category: cleanup
bugzilla: https://gitee.com/openeuler/kernel/issues/IAHY3K

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e03c16fb4af1dfc615a4e1f51be0d5fe5840b904

--------------------------------

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: default avatarPankaj Raghav <p.raghav@samsung.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Conflicts:
	mm/readahead.c
[ Context conflicts. ]
Signed-off-by: default avatarLiu Shixin <liushixin2@huawei.com>
parent 75c34cab

mm/readahead.c

+2 −4
Original line number Diff line number Diff line
@@ -508,10 +508,8 @@ void page_cache_ra_order(struct readahead_control *ractl, 


	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));

	}



	/* See comment in page_cache_ra_unbounded() */