[PATCH v2] md: Kill usage of page->index

From: Kent Overstreet <hidden>
Date: 2021-10-14 14:30:31
Also in: linux-mm, linux-raid, lkml
Subsystem: software raid (multiple disks) support, the rest · Maintainers: Song Liu, Yu Kuai, Linus Torvalds

On Thu, Oct 14, 2021 at 04:58:46PM +0800, heming.zhao@suse.com wrote:

Hello all,

The page->index takes an important role for cluster-md module.
i.e, a two-node HA env, node A bitmap may be managed in first 4K area, then
node B bitmap is in 8K area (the second page). this patch removes the index
and fix/hardcode index with value 0, which will only operate first node bitmap.

If this serial patches are important and must be merged in mainline, we should
redesign code logic for the related code.

Thanks,
Heming

Can you look at and test the updated patch below? The more I look at the md
bitmap code the more it scares me.

-- >8 --
Subject: [PATCH] md: Kill usage of page->index

As part of the struct page cleanups underway, we want to remove as much
usage of page->mapping and page->index as possible, as frequently they
are known from context - as they are here in the md bitmap code.

Signed-off-by: Kent Overstreet <redacted>
---
 drivers/md/md-bitmap.c | 49 ++++++++++++++++++++----------------------
 drivers/md/md-bitmap.h |  1 +
 2 files changed, 24 insertions(+), 26 deletions(-)

diff --git a/drivers/md/md-bitmap.c b/drivers/md/md-bitmap.c
index e29c6298ef..316e4cd5a7 100644
--- a/drivers/md/md-bitmap.c
+++ b/drivers/md/md-bitmap.c

@@ -165,10 +165,8 @@ static int read_sb_page(struct mddev *mddev, loff_t offset,
 
 		if (sync_page_io(rdev, target,
 				 roundup(size, bdev_logical_block_size(rdev->bdev)),
-				 page, REQ_OP_READ, 0, true)) {
-			page->index = index;
+				 page, REQ_OP_READ, 0, true))
 			return 0;
-		}
 	}
 	return -EIO;
 }

@@ -209,7 +207,8 @@ static struct md_rdev *next_active_rdev(struct md_rdev *rdev, struct mddev *mdde
 	return NULL;
 }
 
-static int write_sb_page(struct bitmap *bitmap, struct page *page, int wait)
+static int write_sb_page(struct bitmap *bitmap, struct page *page,
+			 unsigned long index, int wait)
 {
 	struct md_rdev *rdev;
 	struct block_device *bdev;

@@ -224,7 +223,7 @@ static int write_sb_page(struct bitmap *bitmap, struct page *page, int wait)
 
 		bdev = (rdev->meta_bdev) ? rdev->meta_bdev : rdev->bdev;
 
-		if (page->index == store->file_pages-1) {
+		if (index == store->file_pages-1) {
 			int last_page_size = store->bytes & (PAGE_SIZE-1);
 			if (last_page_size == 0)
 				last_page_size = PAGE_SIZE;

@@ -236,8 +235,7 @@ static int write_sb_page(struct bitmap *bitmap, struct page *page, int wait)
 		 */
 		if (mddev->external) {
 			/* Bitmap could be anywhere. */
-			if (rdev->sb_start + offset + (page->index
-						       * (PAGE_SIZE/512))
+			if (rdev->sb_start + offset + index * PAGE_SECTORS
 			    > rdev->data_offset
 			    &&
 			    rdev->sb_start + offset

@@ -247,7 +245,7 @@ static int write_sb_page(struct bitmap *bitmap, struct page *page, int wait)
 		} else if (offset < 0) {
 			/* DATA  BITMAP METADATA  */
 			if (offset
-			    + (long)(page->index * (PAGE_SIZE/512))
+			    + (long)(index * PAGE_SECTORS)
 			    + size/512 > 0)
 				/* bitmap runs in to metadata */
 				goto bad_alignment;

@@ -259,7 +257,7 @@ static int write_sb_page(struct bitmap *bitmap, struct page *page, int wait)
 			/* METADATA BITMAP DATA */
 			if (rdev->sb_start
 			    + offset
-			    + page->index*(PAGE_SIZE/512) + size/512
+			    + index * PAGE_SECTORS + size/512
 			    > rdev->data_offset)
 				/* bitmap runs in to data */
 				goto bad_alignment;

@@ -268,7 +266,7 @@ static int write_sb_page(struct bitmap *bitmap, struct page *page, int wait)
 		}
 		md_super_write(mddev, rdev,
 			       rdev->sb_start + offset
-			       + page->index * (PAGE_SIZE/512),
+			       + index * PAGE_SECTORS,
 			       size,
 			       page);
 	}

@@ -285,12 +283,13 @@ static void md_bitmap_file_kick(struct bitmap *bitmap);
 /*
  * write out a page to a file
  */
-static void write_page(struct bitmap *bitmap, struct page *page, int wait)
+static void write_page(struct bitmap *bitmap, struct page *page,
+		       unsigned long index, int wait)
 {
 	struct buffer_head *bh;
 
 	if (bitmap->storage.file == NULL) {
-		switch (write_sb_page(bitmap, page, wait)) {
+		switch (write_sb_page(bitmap, page, index, wait)) {
 		case -EINVAL:
 			set_bit(BITMAP_WRITE_ERROR, &bitmap->flags);
 		}

@@ -399,7 +398,6 @@ static int read_page(struct file *file, unsigned long index,
 		blk_cur++;
 		bh = bh->b_this_page;
 	}
-	page->index = index;
 
 	wait_event(bitmap->write_wait,
 		   atomic_read(&bitmap->pending_writes)==0);

@@ -472,7 +470,7 @@ void md_bitmap_update_sb(struct bitmap *bitmap)
 	sb->sectors_reserved = cpu_to_le32(bitmap->mddev->
 					   bitmap_info.space);
 	kunmap_atomic(sb);
-	write_page(bitmap, bitmap->storage.sb_page, 1);
+	write_page(bitmap, bitmap->storage.sb_page, bitmap->storage.sb_index, 1);
 }
 EXPORT_SYMBOL(md_bitmap_update_sb);

@@ -524,7 +522,6 @@ static int md_bitmap_new_disk_sb(struct bitmap *bitmap)
 	bitmap->storage.sb_page = alloc_page(GFP_KERNEL | __GFP_ZERO);
 	if (bitmap->storage.sb_page == NULL)
 		return -ENOMEM;
-	bitmap->storage.sb_page->index = 0;
 
 	sb = kmap_atomic(bitmap->storage.sb_page);

@@ -776,7 +773,7 @@ static int md_bitmap_storage_alloc(struct bitmap_storage *store,
 				   unsigned long chunks, int with_super,
 				   int slot_number)
 {
-	int pnum, offset = 0;
+	int pnum;
 	unsigned long num_pages;
 	unsigned long bytes;

@@ -785,7 +782,7 @@ static int md_bitmap_storage_alloc(struct bitmap_storage *store,
 		bytes += sizeof(bitmap_super_t);
 
 	num_pages = DIV_ROUND_UP(bytes, PAGE_SIZE);
-	offset = slot_number * num_pages;
+	store->sb_index = slot_number * num_pages;
 
 	store->filemap = kmalloc_array(num_pages, sizeof(struct page *),
 				       GFP_KERNEL);

@@ -802,7 +799,6 @@ static int md_bitmap_storage_alloc(struct bitmap_storage *store,
 	if (store->sb_page) {
 		store->filemap[0] = store->sb_page;
 		pnum = 1;
-		store->sb_page->index = offset;
 	}
 
 	for ( ; pnum < num_pages; pnum++) {

@@ -811,7 +807,6 @@ static int md_bitmap_storage_alloc(struct bitmap_storage *store,
 			store->file_pages = pnum;
 			return -ENOMEM;
 		}
-		store->filemap[pnum]->index = pnum + offset;
 	}
 	store->file_pages = pnum;

@@ -929,6 +924,7 @@ static void md_bitmap_file_set_bit(struct bitmap *bitmap, sector_t block)
 	unsigned long chunk = block >> bitmap->counts.chunkshift;
 	struct bitmap_storage *store = &bitmap->storage;
 	unsigned long node_offset = 0;
+	unsigned long index = file_page_index(store, chunk);
 
 	if (mddev_is_clustered(bitmap->mddev))
 		node_offset = bitmap->cluster_slot * store->file_pages;

@@ -945,9 +941,9 @@ static void md_bitmap_file_set_bit(struct bitmap *bitmap, sector_t block)
 	else
 		set_bit_le(bit, kaddr);
 	kunmap_atomic(kaddr);
-	pr_debug("set file bit %lu page %lu\n", bit, page->index);
+	pr_debug("set file bit %lu page %lu\n", bit, index);
 	/* record page number so it gets flushed to disk when unplug occurs */
-	set_page_attr(bitmap, page->index - node_offset, BITMAP_PAGE_DIRTY);
+	set_page_attr(bitmap, index - node_offset, BITMAP_PAGE_DIRTY);
 }
 
 static void md_bitmap_file_clear_bit(struct bitmap *bitmap, sector_t block)

@@ -958,6 +954,7 @@ static void md_bitmap_file_clear_bit(struct bitmap *bitmap, sector_t block)
 	unsigned long chunk = block >> bitmap->counts.chunkshift;
 	struct bitmap_storage *store = &bitmap->storage;
 	unsigned long node_offset = 0;
+	unsigned long index = file_page_index(store, chunk);
 
 	if (mddev_is_clustered(bitmap->mddev))
 		node_offset = bitmap->cluster_slot * store->file_pages;

@@ -972,8 +969,8 @@ static void md_bitmap_file_clear_bit(struct bitmap *bitmap, sector_t block)
 	else
 		clear_bit_le(bit, paddr);
 	kunmap_atomic(paddr);
-	if (!test_page_attr(bitmap, page->index - node_offset, BITMAP_PAGE_NEEDWRITE)) {
-		set_page_attr(bitmap, page->index - node_offset, BITMAP_PAGE_PENDING);
+	if (!test_page_attr(bitmap, index - node_offset, BITMAP_PAGE_NEEDWRITE)) {
+		set_page_attr(bitmap, index - node_offset, BITMAP_PAGE_PENDING);
 		bitmap->allclean = 0;
 	}
 }

@@ -1027,7 +1024,7 @@ void md_bitmap_unplug(struct bitmap *bitmap)
 							  "md bitmap_unplug");
 			}
 			clear_page_attr(bitmap, i, BITMAP_PAGE_PENDING);
-			write_page(bitmap, bitmap->storage.filemap[i], 0);
+			write_page(bitmap, bitmap->storage.filemap[i], i, 0);
 			writing = 1;
 		}
 	}

@@ -1137,7 +1134,7 @@ static int md_bitmap_init_from_disk(struct bitmap *bitmap, sector_t start)
 				memset(paddr + offset, 0xff,
 				       PAGE_SIZE - offset);
 				kunmap_atomic(paddr);
-				write_page(bitmap, page, 1);
+				write_page(bitmap, page, index, 1);
 
 				ret = -EIO;
 				if (test_bit(BITMAP_WRITE_ERROR,

@@ -1336,7 +1333,7 @@ void md_bitmap_daemon_work(struct mddev *mddev)
 		if (bitmap->storage.filemap &&
 		    test_and_clear_page_attr(bitmap, j,
 					     BITMAP_PAGE_NEEDWRITE)) {
-			write_page(bitmap, bitmap->storage.filemap[j], 0);
+			write_page(bitmap, bitmap->storage.filemap[j], j, 0);
 		}
 	}

diff --git a/drivers/md/md-bitmap.h b/drivers/md/md-bitmap.h
index cfd7395de8..6e820eea32 100644
--- a/drivers/md/md-bitmap.h
+++ b/drivers/md/md-bitmap.h

@@ -207,6 +207,7 @@ struct bitmap {
 						 * w/ filemap pages */
 		unsigned long file_pages;	/* number of pages in the file*/
 		unsigned long bytes;		/* total bytes in the bitmap */
+		unsigned long sb_index;		/* sb page index */
 	} storage;
 
 	unsigned long flags;

-- 
2.33.0

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