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Date:   Fri, 15 Oct 2021 11:01:21 +0800
From:   Guoqing Jiang <guoqing.jiang@...ux.dev>
To:     Kent Overstreet <kent.overstreet@...il.com>,
        "heming.zhao@...e.com" <heming.zhao@...e.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, linux-raid@...r.kernel.org,
        linux-block@...r.kernel.org, axboe@...nel.dk,
        alexander.h.duyck@...ux.intel.com
Subject: Re: [PATCH v2] md: Kill usage of page->index



On 10/14/21 10:30 PM, Kent Overstreet wrote:
> On Thu, Oct 14, 2021 at 04:58:46PM +0800,heming.zhao@...e.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<kent.overstreet@...il.com>
> ---
>   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);

I guess it is fine for sb_page now.

[...]

> @@ -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);

But for filemap page, I am not sure the above is correct.

>   			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);

Ditto.

>   
>   				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);

Ditto.


>   		}
>   	}
>   
> 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 */

I guess it resolve the issue for sb_page, and we might need to do 
similar things
for filemap as well if I am not misunderstood.

Thanks,
Guoqing

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