On Thu, Dec 14, 2023 at 02:27:17PM -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. Shouldn't we put this in __tlb_gather_mmu() which already has the CONFIG_MMU_GATHER_NO_GATHER ifdefs? That would presuambly help with, eg zap_page_range_single() too. > Signed-off-by: Jianfeng Wang <jianfeng.w.wang@xxxxxxxxxx> > --- > mm/mmap.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/mm/mmap.c b/mm/mmap.c > index 1971bfffcc03..da0308eef435 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -2330,7 +2330,10 @@ static void unmap_region(struct mm_struct *mm, struct ma_state *mas, > struct mmu_gather tlb; > unsigned long mt_start = mas->index; > > + /* Defer lru_add_drain() to tlb_finish_mmu() for the ifndef case. */ > +#ifdef 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 +3303,10 @@ void exit_mmap(struct mm_struct *mm) > return; > } > > + /* Defer lru_add_drain() to tlb_finish_mmu() for the ifndef case. */ > +#ifdef CONFIG_MMU_GATHER_NO_GATHER > lru_add_drain(); > +#endif > flush_cache_mm(mm); > tlb_gather_mmu_fullmm(&tlb, mm); > /* update_hiwater_rss(mm) here? but nobody should be looking */ > -- > 2.42.1 > >
