mm/damon/core: set effective quota on first charge window

The effective quota of a scheme is initialized zero, which means there is
no quota.  It is set based on user-specified time/quota/quota goals.  But
the later value set is done only from the second charge window.  As a
result, a scheme having a user-specified quota can work as not having the
quota (unexpectedly fast) for the first charge window.  In practical and
common use cases the quota interval is not too long, and the scheme's
target access pattern is restrictive.  Hence the issue should be modest.
That said, it is apparently an unintended misbehavior.  Fix the problem by
setting esz on the first charge window.

Link: https://lkml.kernel.org/r/20250916032339.115817-3-sj@kernel.org
Fixes: 1cd243030059 ("mm/damon/schemes: implement time quota") # 5.16.x
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/damon/core.c b/mm/damon/core.c
index ff2c6bb306210e3fc062235cc2371b05291c9c2c..775121ae7a9bc9970db0bcc7f8b42daf21e95de6 100644 (file)
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -2142,8 +2142,10 @@ static void damos_adjust_quota(struct damon_ctx *c, struct damos *s)
                return;
 
        /* First charge window */
-       if (!quota->total_charged_sz && !quota->charged_from)
+       if (!quota->total_charged_sz && !quota->charged_from) {
                quota->charged_from = jiffies;
+               damos_set_effective_quota(quota);
+       }
 
        /* New charge window starts */
        if (time_after_eq(jiffies, quota->charged_from +