Re: [PATCH v16.1 0/9] mm / virtio: Provide support for free page reporting

[Hillf Danton <hdanton@sina.com>]

On Thu, 23 Jan 2020 11:20:07 +0100 Alexander Graf wrote:
> 
> The big problem I see is that what I really want from a user's point of 
> view is a tuneable that says "Automatically free clean page cache pages 
> that were not accessed in the last X minutes".

A diff is made on top of 1a4e58cce84e ("mm: introduce MADV_PAGEOUT") without
test in any form, assuming it goes in line with the tunable above but without
"X minutes" taken into account.

[BTW, please take a look at
Content-Type: text/plain; charset="utf-8"; format="flowed"
Content-Transfer-Encoding: base64

and ensure pure text message.]


--- a/include/uapi/asm-generic/mman-common.h
+++ b/include/uapi/asm-generic/mman-common.h
@@ -69,6 +69,7 @@
 
 #define MADV_COLD	20		/* deactivate these pages */
 #define MADV_PAGEOUT	21		/* reclaim these pages */
+#define MADV_CCPC	22		/* reclaim cold & clean page cache pages */
 
 /* compatibility flags */
 #define MAP_FILE	0
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -35,6 +35,7 @@
 struct madvise_walk_private {
 	struct mmu_gather *tlb;
 	bool pageout;
+	int behavior;
 };
 
 /*
@@ -50,6 +51,7 @@ static int madvise_need_mmap_write(int b
 	case MADV_DONTNEED:
 	case MADV_COLD:
 	case MADV_PAGEOUT:
+	case MADV_CCPC:
 	case MADV_FREE:
 		return 0;
 	default:
@@ -304,6 +306,7 @@ static int madvise_cold_or_pageout_pte_r
 	struct madvise_walk_private *private = walk->private;
 	struct mmu_gather *tlb = private->tlb;
 	bool pageout = private->pageout;
+	bool ccpc = private->behavior == MADV_CCPC;
 	struct mm_struct *mm = tlb->mm;
 	struct vm_area_struct *vma = walk->vma;
 	pte_t *orig_pte, *pte, ptent;
@@ -429,6 +432,8 @@ regular_page:
 		VM_BUG_ON_PAGE(PageTransCompound(page), page);
 
 		if (pte_young(ptent)) {
+			if (ccpc)
+				continue;
 			ptent = ptep_get_and_clear_full(mm, addr, pte,
 							tlb->fullmm);
 			ptent = pte_mkold(ptent);
@@ -436,6 +441,10 @@ regular_page:
 			tlb_remove_tlb_entry(tlb, pte, addr);
 		}
 
+		if (ccpc)
+			if (PageDirty(page))
+				continue;
+
 		/*
 		 * We are deactivating a page for accelerating reclaiming.
 		 * VM couldn't reclaim the page unless we clear PG_young.
@@ -502,12 +511,13 @@ static long madvise_cold(struct vm_area_
 }
 
 static void madvise_pageout_page_range(struct mmu_gather *tlb,
-			     struct vm_area_struct *vma,
+			     struct vm_area_struct *vma, int behavior,
 			     unsigned long addr, unsigned long end)
 {
 	struct madvise_walk_private walk_private = {
 		.pageout = true,
 		.tlb = tlb,
+		.behavior = behavior,
 	};
 
 	tlb_start_vma(tlb, vma);
@@ -515,10 +525,10 @@ static void madvise_pageout_page_range(s
 	tlb_end_vma(tlb, vma);
 }
 
-static inline bool can_do_pageout(struct vm_area_struct *vma)
+static inline bool can_do_pageout(struct vm_area_struct *vma, int behavior)
 {
 	if (vma_is_anonymous(vma))
-		return true;
+		return behavior != MADV_CCPC;
 	if (!vma->vm_file)
 		return false;
 	/*
@@ -531,7 +541,7 @@ static inline bool can_do_pageout(struct
 		inode_permission(file_inode(vma->vm_file), MAY_WRITE) == 0;
 }
 
-static long madvise_pageout(struct vm_area_struct *vma,
+static long madvise_pageout(struct vm_area_struct *vma, int behavior,
 			struct vm_area_struct **prev,
 			unsigned long start_addr, unsigned long end_addr)
 {
@@ -542,12 +552,12 @@ static long madvise_pageout(struct vm_ar
 	if (!can_madv_lru_vma(vma))
 		return -EINVAL;
 
-	if (!can_do_pageout(vma))
+	if (!can_do_pageout(vma, behavior))
 		return 0;
 
 	lru_add_drain();
 	tlb_gather_mmu(&tlb, mm, start_addr, end_addr);
-	madvise_pageout_page_range(&tlb, vma, start_addr, end_addr);
+	madvise_pageout_page_range(&tlb, vma, behavior, start_addr, end_addr);
 	tlb_finish_mmu(&tlb, start_addr, end_addr);
 
 	return 0;
@@ -936,7 +946,8 @@ madvise_vma(struct vm_area_struct *vma,
 	case MADV_COLD:
 		return madvise_cold(vma, prev, start, end);
 	case MADV_PAGEOUT:
-		return madvise_pageout(vma, prev, start, end);
+	case MADV_CCPC:
+		return madvise_pageout(vma, behavior, prev, start, end);
 	case MADV_FREE:
 	case MADV_DONTNEED:
 		return madvise_dontneed_free(vma, prev, start, end, behavior);
@@ -960,6 +971,7 @@ madvise_behavior_valid(int behavior)
 	case MADV_FREE:
 	case MADV_COLD:
 	case MADV_PAGEOUT:
+	case MADV_CCPC:
 #ifdef CONFIG_KSM
 	case MADV_MERGEABLE:
 	case MADV_UNMERGEABLE:
--