mm/writeback: minor clean up for highmem_dirtyable_memory

Since commit a804552b9a15 ("mm/page-writeback.c: fix
dirty_balance_reserve subtraction from dirtyable memory"), local
variable x can not be negative.  And it can not overflow when it is the
total number of dirtyable highmem pages.  Thus remove the unneeded
comment and overflow check.

Link: https://lkml.kernel.org/r/20220224115416.46089-1-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 91d163f..f13ed76 100644 (file)
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -324,18 +324,6 @@ static unsigned long highmem_dirtyable_memory(unsigned long total)
        }
 
        /*
-        * Unreclaimable memory (kernel memory or anonymous memory
-        * without swap) can bring down the dirtyable pages below
-        * the zone's dirty balance reserve and the above calculation
-        * will underflow.  However we still want to add in nodes
-        * which are below threshold (negative values) to get a more
-        * accurate calculation but make sure that the total never
-        * underflows.
-        */
-       if ((long)x < 0)
-               x = 0;
-
-       /*
         * Make sure that the number of highmem pages is never larger
         * than the number of the total dirtyable memory. This can only
         * occur in very strange VM situations but we want to make sure