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Shutemov" Subject: Re: [PATCH v4 4/4] mm: introduce MADV_PAGEOUT Message-ID: <20190712135809.GB31107@cmpxchg.org> References: <20190711012528.176050-1-minchan@kernel.org> <20190711012528.176050-5-minchan@kernel.org> <20190711184223.GD20341@cmpxchg.org> <20190712051828.GA128252@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190712051828.GA128252@google.com> User-Agent: Mutt/1.12.0 (2019-05-25) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 12, 2019 at 02:18:28PM +0900, Minchan Kim wrote: > Hi Johannes, > > On Thu, Jul 11, 2019 at 02:42:23PM -0400, Johannes Weiner wrote: > > On Thu, Jul 11, 2019 at 10:25:28AM +0900, Minchan Kim wrote: > > > @@ -480,6 +482,198 @@ static long madvise_cold(struct vm_area_struct *vma, > > > return 0; > > > } > > > > > > +static int madvise_pageout_pte_range(pmd_t *pmd, unsigned long addr, > > > + unsigned long end, struct mm_walk *walk) > > > +{ > > > + struct mmu_gather *tlb = walk->private; > > > + struct mm_struct *mm = tlb->mm; > > > + struct vm_area_struct *vma = walk->vma; > > > + pte_t *orig_pte, *pte, ptent; > > > + spinlock_t *ptl; > > > + LIST_HEAD(page_list); > > > + struct page *page; > > > + unsigned long next; > > > + > > > + if (fatal_signal_pending(current)) > > > + return -EINTR; > > > + > > > + next = pmd_addr_end(addr, end); > > > + if (pmd_trans_huge(*pmd)) { > > > + pmd_t orig_pmd; > > > + > > > + tlb_change_page_size(tlb, HPAGE_PMD_SIZE); > > > + ptl = pmd_trans_huge_lock(pmd, vma); > > > + if (!ptl) > > > + return 0; > > > + > > > + orig_pmd = *pmd; > > > + if (is_huge_zero_pmd(orig_pmd)) > > > + goto huge_unlock; > > > + > > > + if (unlikely(!pmd_present(orig_pmd))) { > > > + VM_BUG_ON(thp_migration_supported() && > > > + !is_pmd_migration_entry(orig_pmd)); > > > + goto huge_unlock; > > > + } > > > + > > > + page = pmd_page(orig_pmd); > > > + if (next - addr != HPAGE_PMD_SIZE) { > > > + int err; > > > + > > > + if (page_mapcount(page) != 1) > > > + goto huge_unlock; > > > + get_page(page); > > > + spin_unlock(ptl); > > > + lock_page(page); > > > + err = split_huge_page(page); > > > + unlock_page(page); > > > + put_page(page); > > > + if (!err) > > > + goto regular_page; > > > + return 0; > > > + } > > > + > > > + if (isolate_lru_page(page)) > > > + goto huge_unlock; > > > + > > > + if (pmd_young(orig_pmd)) { > > > + pmdp_invalidate(vma, addr, pmd); > > > + orig_pmd = pmd_mkold(orig_pmd); > > > + > > > + set_pmd_at(mm, addr, pmd, orig_pmd); > > > + tlb_remove_tlb_entry(tlb, pmd, addr); > > > + } > > > + > > > + ClearPageReferenced(page); > > > + test_and_clear_page_young(page); > > > + list_add(&page->lru, &page_list); > > > +huge_unlock: > > > + spin_unlock(ptl); > > > + reclaim_pages(&page_list); > > > + return 0; > > > + } > > > + > > > + if (pmd_trans_unstable(pmd)) > > > + return 0; > > > +regular_page: > > > + tlb_change_page_size(tlb, PAGE_SIZE); > > > + orig_pte = pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl); > > > + flush_tlb_batched_pending(mm); > > > + arch_enter_lazy_mmu_mode(); > > > + for (; addr < end; pte++, addr += PAGE_SIZE) { > > > + ptent = *pte; > > > + if (!pte_present(ptent)) > > > + continue; > > > + > > > + page = vm_normal_page(vma, addr, ptent); > > > + if (!page) > > > + continue; > > > + > > > + /* > > > + * creating a THP page is expensive so split it only if we > > > + * are sure it's worth. Split it if we are only owner. > > > + */ > > > + if (PageTransCompound(page)) { > > > + if (page_mapcount(page) != 1) > > > + break; > > > + get_page(page); > > > + if (!trylock_page(page)) { > > > + put_page(page); > > > + break; > > > + } > > > + pte_unmap_unlock(orig_pte, ptl); > > > + if (split_huge_page(page)) { > > > + unlock_page(page); > > > + put_page(page); > > > + pte_offset_map_lock(mm, pmd, addr, &ptl); > > > + break; > > > + } > > > + unlock_page(page); > > > + put_page(page); > > > + pte = pte_offset_map_lock(mm, pmd, addr, &ptl); > > > + pte--; > > > + addr -= PAGE_SIZE; > > > + continue; > > > + } > > > + > > > + VM_BUG_ON_PAGE(PageTransCompound(page), page); > > > + > > > + if (isolate_lru_page(page)) > > > + continue; > > > + > > > + if (pte_young(ptent)) { > > > + ptent = ptep_get_and_clear_full(mm, addr, pte, > > > + tlb->fullmm); > > > + ptent = pte_mkold(ptent); > > > + set_pte_at(mm, addr, pte, ptent); > > > + tlb_remove_tlb_entry(tlb, pte, addr); > > > + } > > > + ClearPageReferenced(page); > > > + test_and_clear_page_young(page); > > > + list_add(&page->lru, &page_list); > > > + } > > > + > > > + arch_leave_lazy_mmu_mode(); > > > + pte_unmap_unlock(orig_pte, ptl); > > > + reclaim_pages(&page_list); > > > + cond_resched(); > > > + > > > + return 0; > > > +} > > > > I know you have briefly talked about code sharing already. > > > > While I agree that sharing with MADV_FREE is maybe a stretch, I > > applied these patches and compared the pageout and the cold page table > > functions, and they are line for line the same EXCEPT for 2-3 lines at > > the very end, where one reclaims and the other deactivates. It would > > be good to share here, it shouldn't be hard or result in fragile code. > > Fair enough if we leave MADV_FREE. > > > > > Something like int madvise_cold_or_pageout_range(..., bool pageout)? > > How about this? > > From 41592f23e876ec21e49dc3c76dc89538e2bb16be Mon Sep 17 00:00:00 2001 > From: Minchan Kim > Date: Fri, 12 Jul 2019 14:05:36 +0900 > Subject: [PATCH] mm: factor out common parts between MADV_COLD and > MADV_PAGEOUT > > There are many common parts between MADV_COLD and MADV_PAGEOUT. > This patch factor them out to save code duplication. > > Signed-off-by: Minchan Kim This looks much better, thanks! > @@ -423,6 +445,12 @@ static int madvise_cold_pte_range(pmd_t *pmd, unsigned long addr, > > VM_BUG_ON_PAGE(PageTransCompound(page), page); > > + if (pageout) { > + if (isolate_lru_page(page)) > + continue; > + list_add(&page->lru, &page_list); > + } > + > if (pte_young(ptent)) { > ptent = ptep_get_and_clear_full(mm, addr, pte, > tlb->fullmm); One thought on the ordering here. When LRU isolation fails, it would still make sense to clear the young bit: we cannot reclaim the page as we wanted to, but the user still provided a clear hint that the page is cold and she won't be touching it for a while. MADV_PAGEOUT is basically MADV_COLD + try_to_reclaim. So IMO isolation should go to the end next to deactivate_page().