Hello Yu Zhao,
The patch 081488051d28: "mm/mglru: fix underprotected page cache"
from Dec 7, 2023 (linux-next), leads to the following Smatch static
checker warning:
mm/workingset.c:318 lru_gen_refault()
warn: always true condition '(refs >= ((((1))) << (__builtin_choose_expr((4 == 4), (((2) < (64 - 26 - 3 - 3 - 0 - 10 - 0 - (8 + 14))) ?(2):(64 - 26 - 3 - 3 - 0 - 10 - 0 - (8 + 14))), ))) - 1) => (s32min-s32max >= 0)'
mm/workingset.c
308 atomic_long_add(delta, &lrugen->refaulted[hist][type][tier]);
309 mod_lruvec_state(lruvec, WORKINGSET_ACTIVATE_BASE + type, delta);
310
311 /*
312 * Count the following two cases as stalls:
313 * 1. For pages accessed through page tables, hotter pages pushed out
314 * hot pages which refaulted immediately.
315 * 2. For pages accessed multiple times through file descriptors,
316 * they would have been protected by sort_folio().
317 */
--> 318 if (lru_gen_in_fault() || refs >= BIT(LRU_REFS_WIDTH) - 1) {
^^^^^^^^^^^^^^^^^^^^^^^
In my x86 allmodconfig this is zero and refs is always >= 0. This could
be intentional, but I thought it was worth checking.
319 set_mask_bits(&folio->flags, 0, LRU_REFS_MASK | BIT(PG_workingset));
320 mod_lruvec_state(lruvec, WORKINGSET_RESTORE_BASE + type, delta);
321 }
322 unlock:
323 rcu_read_unlock();
324 }
regards,
dan carpenter
