criu: pagemap: add entries for zero pages

The pages that are mapped to zero_page_pfn are not dumped but information
where are they located is required for lazy restore.
Note that get_pagemap users presumed that zero pages are not a part of the
pagemap and these pages were just silently skipped during memory restore.
At the moment I preserve this semantics and force get_pagemap to skip zero
pages.
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

criu/include/page-pipe.h

@@ -101,6 +101,9 @@ struct page_pipe_buf {
 	struct list_head l;	/* links into page_pipe->bufs */
 };
 
+#define PP_HOLE_PARENT (1 << 0)
+#define PP_HOLE_ZERO   (1 << 1)
+
 struct page_pipe {
 	unsigned int nr_pipes;	/* how many page_pipe_bufs in there */
 	struct list_head bufs;	/* list of bufs */
@@ -113,6 +116,7 @@ struct page_pipe {
 	unsigned int nr_holes;	/* number of holes allocated */
 	unsigned int free_hole;	/* number of holes in use */
 	struct iovec *holes;	/* holes */
+	unsigned int *hole_flags;
 	unsigned flags;		/* PP_FOO flags below */
 };
 
@@ -124,7 +128,8 @@ struct page_pipe *create_page_pipe(unsigned int nr_segs, struct iovec *iovs, uns
 extern void destroy_page_pipe(struct page_pipe *p);
 extern int page_pipe_add_page(struct page_pipe *p, unsigned long addr,
 			      unsigned int flags);
-extern int page_pipe_add_hole(struct page_pipe *p, unsigned long addr);
+extern int page_pipe_add_hole(struct page_pipe *pp, unsigned long addr,
+			      unsigned int flags);
 
 extern void debug_show_page_pipe(struct page_pipe *pp);
 void page_pipe_reinit(struct page_pipe *pp);

criu/include/page-xfer.h

@@ -16,7 +16,7 @@ struct page_xfer {
 	/* transfers pages related to previous pagemap */
 	int (*write_pages)(struct page_xfer *self, int pipe, unsigned long len);
 	/* transfers one hole -- vaddr:len entry w/o pages */
-	int (*write_hole)(struct page_xfer *self, struct iovec *iov);
+	int (*write_hole)(struct page_xfer *self, struct iovec *iov, int type);
 	void (*close)(struct page_xfer *self);
 
 	/* private data for every page-xfer engine */

criu/include/stats.h

@@ -25,6 +25,7 @@ enum {
 	CNT_PAGES_SCANNED,
 	CNT_PAGES_SKIPPED_PARENT,
 	CNT_PAGES_WRITTEN,
+	CNT_PAGES_ZERO,
 
 	DUMP_CNT_NR_STATS,
 };

criu/mem.c

@@ -109,14 +109,17 @@ bool should_dump_page(VmaEntry *vmae, u64 pme)
 		return false;
 	if (vma_entry_is(vmae, VMA_AREA_AIORING))
 		return true;
-	if (pme & PME_SWAP)
-		return true;
-	if ((pme & PME_PRESENT) && ((pme & PME_PFRAME_MASK) != kdat.zero_page_pfn))
+	if (pme & (PME_PRESENT | PME_SWAP))
 		return true;
 
 	return false;
 }
 
+static inline bool page_is_zero(u64 pme)
+{
+	return (pme & PME_PFRAME_MASK) == kdat.zero_page_pfn;
+}
+
 bool page_in_parent(bool dirty)
 {
 	/*
@@ -140,7 +143,7 @@ static int generate_iovs(struct vma_area *vma, struct page_pipe *pp, u64 *map, u
 {
 	u64 *at = &map[PAGE_PFN(*off)];
 	unsigned long pfn, nr_to_scan;
-	unsigned long pages[2] = {};
+	unsigned long pages[3] = {};
 
 	nr_to_scan = (vma_area_len(vma) - *off) / PAGE_SIZE;
 
@@ -164,12 +167,15 @@ static int generate_iovs(struct vma_area *vma, struct page_pipe *pp, u64 *map, u
 		 * page. The latter would be checked in page-xfer.
 		 */
 
-		if (has_parent && page_in_parent(at[pfn] & PME_SOFT_DIRTY)) {
-			ret = page_pipe_add_hole(pp, vaddr);
+		if (page_is_zero(at[pfn])) {
+			ret = page_pipe_add_hole(pp, vaddr, PP_HOLE_ZERO);
 			pages[0]++;
+		} else if (has_parent && page_in_parent(at[pfn] & PME_SOFT_DIRTY)) {
+			ret = page_pipe_add_hole(pp, vaddr, PP_HOLE_PARENT);
+			pages[1]++;
 		} else {
 			ret = page_pipe_add_page(pp, vaddr, ppb_flags);
-			pages[1]++;
+			pages[2]++;
 		}
 
 		if (ret) {
@@ -181,10 +187,12 @@ static int generate_iovs(struct vma_area *vma, struct page_pipe *pp, u64 *map, u
 	*off += pfn * PAGE_SIZE;
 
 	cnt_add(CNT_PAGES_SCANNED, nr_to_scan);
-	cnt_add(CNT_PAGES_SKIPPED_PARENT, pages[0]);
-	cnt_add(CNT_PAGES_WRITTEN, pages[1]);
+	cnt_add(CNT_PAGES_ZERO, pages[0]);
+	cnt_add(CNT_PAGES_SKIPPED_PARENT, pages[1]);
+	cnt_add(CNT_PAGES_WRITTEN, pages[2]);
 
-	pr_info("Pagemap generated: %lu pages %lu holes\n", pages[1], pages[0]);
+	pr_info("Pagemap generated: %lu pages %lu holes %lu zeros\n",
+		pages[2], pages[1], pages[0]);
 	return 0;
 }
 

criu/page-pipe.c

@@ -269,7 +269,8 @@ int page_pipe_add_page(struct page_pipe *pp, unsigned long addr,
 
 #define PP_HOLES_BATCH	32
 
-int page_pipe_add_hole(struct page_pipe *pp, unsigned long addr)
+int page_pipe_add_hole(struct page_pipe *pp, unsigned long addr,
+		       unsigned int flags)
 {
 	if (pp->free_hole >= pp->nr_holes) {
 		pp->holes = xrealloc(pp->holes,
@@ -277,15 +278,23 @@ int page_pipe_add_hole(struct page_pipe *pp, unsigned long addr)
 		if (!pp->holes)
 			return -1;
 
+		pp->hole_flags = xrealloc(pp->hole_flags,
+					  (pp->nr_holes + PP_HOLES_BATCH) * sizeof(unsigned int));
+		if(!pp->hole_flags)
+			return -1;
+
 		pp->nr_holes += PP_HOLES_BATCH;
 	}
 
 	if (pp->free_hole &&
-			iov_grow_page(&pp->holes[pp->free_hole - 1], addr))
+	    pp->hole_flags[pp->free_hole - 1] == flags &&
+	    iov_grow_page(&pp->holes[pp->free_hole - 1], addr))
 		goto out;
 
 	iov_init(&pp->holes[pp->free_hole++], addr);
 
+	pp->hole_flags[pp->free_hole - 1] = flags;
+
 out:
 	return 0;
 }

criu/page-xfer.c

@@ -38,6 +38,7 @@ static void psi2iovec(struct page_server_iov *ps, struct iovec *iov)
 #define PS_IOV_OPEN	3
 #define PS_IOV_OPEN2	4
 #define PS_IOV_PARENT	5
+#define PS_IOV_ZERO	6
 
 #define PS_IOV_FLUSH		0x1023
 #define PS_IOV_FLUSH_N_CLOSE	0x1024
@@ -149,9 +150,10 @@ static int write_pages_to_server(struct page_xfer *xfer,
 	return 0;
 }
 
-static int write_hole_to_server(struct page_xfer *xfer, struct iovec *iov)
+static int write_hole_to_server(struct page_xfer *xfer, struct iovec *iov,
+				int type)
 {
-	return send_iov(xfer->sk, PS_IOV_HOLE, xfer->dst_id, iov);
+	return send_iov(xfer->sk, type, xfer->dst_id, iov);
 }
 
 static void close_server_xfer(struct page_xfer *xfer)
@@ -276,25 +278,36 @@ static int check_pagehole_in_parent(struct page_read *p, struct iovec *iov)
 	}
 }
 
-static int write_pagehole_loc(struct page_xfer *xfer, struct iovec *iov)
+static int write_hole_loc(struct page_xfer *xfer, struct iovec *iov, int type)
 {
 	PagemapEntry pe = PAGEMAP_ENTRY__INIT;
 
-	if (xfer->parent != NULL) {
-		int ret;
+	pe.vaddr = encode_pointer(iov->iov_base);
+	pe.nr_pages = iov->iov_len / PAGE_SIZE;
 
-		ret = check_pagehole_in_parent(xfer->parent, iov);
-		if (ret) {
-			pr_err("Hole %p/%zu not found in parent\n",
-					iov->iov_base, iov->iov_len);
-			return -1;
+	switch (type) {
+	case PS_IOV_HOLE:
+		if (xfer->parent != NULL) {
+			int ret;
+
+			ret = check_pagehole_in_parent(xfer->parent, iov);
+			if (ret) {
+				pr_err("Hole %p/%zu not found in parent\n",
+				       iov->iov_base, iov->iov_len);
+				return -1;
+			}
 		}
-	}
 
-	pe.vaddr = encode_pointer(iov->iov_base);
-	pe.nr_pages = iov->iov_len / PAGE_SIZE;
-	pe.has_in_parent = true;
-	pe.in_parent = true;
+		pe.has_in_parent = true;
+		pe.in_parent = true;
+		break;
+	case PS_IOV_ZERO:
+		pe.has_zero = true;
+		pe.zero = true;
+		break;
+	default:
+		return -1;
+	}
 
 	if (pb_write_one(xfer->pmi, &pe, PB_PAGEMAP) < 0)
 		return -1;
@@ -364,7 +377,7 @@ static int open_page_local_xfer(struct page_xfer *xfer, int fd_type, long id)
 out:
 	xfer->write_pagemap = write_pagemap_loc;
 	xfer->write_pages = write_pages_loc;
-	xfer->write_hole = write_pagehole_loc;
+	xfer->write_hole = write_hole_loc;
 	xfer->close = close_page_xfer;
 	return 0;
 }
@@ -378,19 +391,33 @@ int open_page_xfer(struct page_xfer *xfer, int fd_type, long id)
 }
 
 static int page_xfer_dump_hole(struct page_xfer *xfer,
-		struct iovec *hole, unsigned long off)
+			       struct iovec *hole, unsigned long off, int type)
 {
 	BUG_ON(hole->iov_base < (void *)off);
 	hole->iov_base -= off;
 	pr_debug("\th %p [%u]\n", hole->iov_base,
 			(unsigned int)(hole->iov_len / PAGE_SIZE));
 
-	if (xfer->write_hole(xfer, hole))
+	if (xfer->write_hole(xfer, hole, type))
 		return -1;
 
 	return 0;
 }
 
+static int get_hole_type(struct page_pipe *pp, int n)
+{
+	unsigned int hole_flags = pp->hole_flags[n];
+
+	if (hole_flags == PP_HOLE_PARENT)
+		return PS_IOV_HOLE;
+	if (hole_flags == PP_HOLE_ZERO)
+		return PS_IOV_ZERO;
+	else
+		BUG();
+
+	return -1;
+}
+
 static int dump_holes(struct page_xfer *xfer, struct page_pipe *pp,
 		      unsigned int *cur_hole, void *limit, unsigned long off)
 {
@@ -398,11 +425,12 @@ static int dump_holes(struct page_xfer *xfer, struct page_pipe *pp,
 
 	for (; *cur_hole < pp->free_hole ; (*cur_hole)++) {
 		struct iovec hole = pp->holes[*cur_hole];
+		int hole_type = get_hole_type(pp, *cur_hole);
 
 		if (limit && hole.iov_base >= limit)
 			break;
 
-		ret = page_xfer_dump_hole(xfer, &hole, off);
+		ret = page_xfer_dump_hole(xfer, &hole, off, hole_type);
 		if (ret)
 			return ret;
 	}
@@ -655,7 +683,7 @@ static int page_server_hole(int sk, struct page_server_iov *pi)
 		return -1;
 
 	psi2iovec(pi, &iov);
-	if (lxfer->write_hole(lxfer, &iov))
+	if (lxfer->write_hole(lxfer, &iov, pi->cmd))
 		return -1;
 
 	return 0;
@@ -711,6 +739,7 @@ static int page_server_serve(int sk)
 			ret = page_server_add(sk, &pi);
 			break;
 		case PS_IOV_HOLE:
+		case PS_IOV_ZERO:
 			ret = page_server_hole(sk, &pi);
 			break;
 		case PS_IOV_FLUSH:

criu/pagemap.c

@@ -123,13 +123,19 @@ int dedup_one_iovec(struct page_read *pr, unsigned long off, unsigned long len)
 
 static int advance(struct page_read *pr)
 {
-	pr->curr_pme++;
-	if (pr->curr_pme >= pr->nr_pmes)
-		return 0;
+	for (;;) {
+		pr->curr_pme++;
+		if (pr->curr_pme >= pr->nr_pmes)
+			return 0;
+
+		pe = pr->pmes[pr->curr_pme];
+
+		if (!pe->zero)
+			break;
+	}
 
 	pr->pe = pr->pmes[pr->curr_pme];
 	pr->cvaddr = pr->pe->vaddr;
-
 	return 1;
 }
 
@@ -138,7 +144,7 @@ static void skip_pagemap_pages(struct page_read *pr, unsigned long len)
 	if (!len)
 		return;
 
-	if (!pr->pe->in_parent)
+	if (!pr->pe->in_parent && !pr->pe->zero)
 		pr->pi_off += len;
 	pr->cvaddr += len;
 }
@@ -412,6 +418,9 @@ static int read_pagemap_page(struct page_read *pr, unsigned long vaddr, int nr,
 	if (pr->pe->in_parent) {
 		if (read_parent_page(pr, vaddr, nr, buf, flags) < 0)
 			return -1;
+	} else if (pr->pe->zero) {
+		/* zero mappings should be skipped by get_pagemap */
+		BUG();
 	} else {
 		if (maybe_read_page(pr, vaddr, nr, buf, flags) < 0)
 			return -1;

criu/shmem.c

@@ -218,6 +218,8 @@ static void update_shmem_pmaps(struct shmem_info *si, u64 *map, VmaEntry *vma)
 		shmem_pfn = vma_pfn + DIV_ROUND_UP(vma->pgoff, PAGE_SIZE);
 		if (map[vma_pfn] & PME_SOFT_DIRTY)
 			set_pstate(si->pstate_map, shmem_pfn, PST_DIRTY);
+		else if (page_is_zero(map[vma_pfn]))
+			set_pstate(si->pstate_map, shmem_pfn, PST_ZERO);
 		else
 			set_pstate(si->pstate_map, shmem_pfn, PST_DUMP);
 	}
@@ -709,9 +711,9 @@ static int do_dump_one_shmem(int fd, void *addr, struct shmem_info *si)
 		pgaddr = (unsigned long)addr + pfn * PAGE_SIZE;
 again:
 		if (pgstate == PST_ZERO)
-			ret = 0;
+			ret = page_pipe_add_hole(pp, pgaddr, PP_HOLE_ZERO);
 		else if (xfer.parent && page_in_parent(pgstate == PST_DIRTY))
-			ret = page_pipe_add_hole(pp, pgaddr);
+			ret = page_pipe_add_hole(pp, pgaddr, PP_HOLE_PARENT);
 		else
 			ret = page_pipe_add_page(pp, pgaddr, 0);
 

criu/stats.c

@@ -157,6 +157,7 @@ void write_stats(int what)
 		ds_entry.pages_scanned = dstats->counts[CNT_PAGES_SCANNED];
 		ds_entry.pages_skipped_parent = dstats->counts[CNT_PAGES_SKIPPED_PARENT];
 		ds_entry.pages_written = dstats->counts[CNT_PAGES_WRITTEN];
+		ds_entry.pages_zero = dstats->counts[CNT_PAGES_ZERO];
 
 		name = "dump";
 	} else if (what == RESTORE_STATS) {

images/pagemap.proto

@@ -10,4 +10,5 @@ message pagemap_entry {
 	required uint64 vaddr		= 1 [(criu).hex = true];
 	required uint32 nr_pages	= 2;
 	optional bool	in_parent	= 3;
+	optional bool	zero		= 4;
 }

images/stats.proto

@@ -12,6 +12,8 @@ message dump_stats_entry {
 	required uint64			pages_written		= 7;
 
 	optional uint32			irmap_resolve		= 8;
+
+	required uint64			pages_zero		= 9;
 }
 
 message restore_stats_entry {