Yuanchu Xie <[email protected]> writes: > When non-leaf pmd accessed bits are available, MGLRU page table walks > can clear the accessed bit and promptly ignore the accessed bit on the > pte because it's on a different node, so the walk does not update the > generation of said page. When the next scan comes around on the right > node, the non-leaf pmd accessed bit might remain cleared and the pte > accessed bits won't be checked. While this is sufficient for > reclaim-driven aging, where the goal is to select a reasonably cold > page, the access can be missed when aging proactively for measuring the > working set size of a node/memcg. > > Since force_scan disables various other optimizations, we check > force_scan to ignore the non-leaf pmd accessed bit. > > Signed-off-by: Yuanchu Xie <[email protected]> > --- > mm/vmscan.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 4f9c854ce6cc..1a7c7d537db6 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -3522,7 +3522,7 @@ static void walk_pmd_range(pud_t *pud, unsigned long > start, unsigned long end, > > walk->mm_stats[MM_NONLEAF_TOTAL]++; > > - if (should_clear_pmd_young()) { > + if (!walk->force_scan && should_clear_pmd_young()) { > if (!pmd_young(val)) > continue;
Sorry, I don't understand why we need this. If !pmd_young(val), we don't need to update the generation. If pmd_young(val), the bloom filter will be ignored if force_scan == true. Or do I miss something? -- Best Regards, Huang, Ying
