On Tue, 2023-12-12 at 23:28 -0800, Jianfeng Wang wrote: > When unmapping VMA pages, pages will be gathered in batch and released by > tlb_finish_mmu() if CONFIG_MMU_GATHER_NO_GATHER is not set. The function > tlb_finish_mmu() is responsible for calling free_pages_and_swap_cache(), > which calls lru_add_drain() to drain cached pages in folio_batch before > releasing gathered pages. Thus, it is redundant to call lru_add_drain() > before gathering pages, if CONFIG_MMU_GATHER_NO_GATHER is not set. > > Remove lru_add_drain() prior to gathering and unmapping pages in > exit_mmap() and unmap_region() if CONFIG_MMU_GATHER_NO_GATHER is not set. > > Note that the page unmapping process in oom_killer (e.g., in > __oom_reap_task_mm()) also uses tlb_finish_mmu() and does not have > redundant lru_add_drain(). So, this commit makes the code more consistent. > > Signed-off-by: Jianfeng Wang <jianfeng.w.wang@xxxxxxxxxx> > --- > mm/mmap.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/mm/mmap.c b/mm/mmap.c > index 1971bfffcc03..0451285dee4f 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -2330,7 +2330,9 @@ static void unmap_region(struct mm_struct *mm, struct ma_state *mas, > struct mmu_gather tlb; > unsigned long mt_start = mas->index; > > +#ifdef CONFIG_MMU_GATHER_NO_GATHER In your comment you say skip lru_add_drain() when CONFIG_MMU_GATHER_NO_GATHER is *not* set. So shouldn't this be #ifndef CONFIG_MMU_GATHER_NO_GATHER ? > lru_add_drain(); > +#endif > tlb_gather_mmu(&tlb, mm); > update_hiwater_rss(mm); > unmap_vmas(&tlb, mas, vma, start, end, tree_end, mm_wr_locked); > @@ -3300,7 +3302,9 @@ void exit_mmap(struct mm_struct *mm) > return; > } > > +#ifdef CONFIG_MMU_GATHER_NO_GATHER same question as above. > lru_add_drain(); > +#endif > flush_cache_mm(mm); > tlb_gather_mmu_fullmm(&tlb, mm); > /* update_hiwater_rss(mm) here? but nobody should be looking */
