On Thu, Dec 14, 2023 at 03:59:00PM -0800, Jianfeng Wang wrote: > On 12/14/23 3:00 PM, Matthew Wilcox wrote: > > 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. > > > > Thanks. It makes sense to me. > This commit is motivated by a workload that use mmap/unmap heavily. > While the mmu_gather feature is also used by hugetlb, madvise, mprotect, > etc., thus I prefer to have another standalone commit (following this one) > that moves lru_add_drain() to __tlb_gather_mmu() to unify these cases for > not making redundant lru_add_drain() calls when using mmu_gather. That's not normally the approach we take.
