Re: [PATCH 4/5] md: Kill usage of page->index

["heming.zhao@xxxxxxxx" <heming.zhao@xxxxxxxx>]

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

On 10/14/21 16:02, Guoqing Jiang wrote:
> On 10/14/21 12:00 AM, Kent Overstreet wrote:
> > 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@xxxxxxxxx>
> > ---
> >   drivers/md/md-bitmap.c | 44 ++++++++++++++++++++----------------------
> >   1 file changed, 21 insertions(+), 23 deletions(-)
> >
> > diff --git a/drivers/md/md-bitmap.c b/drivers/md/md-bitmap.c
> > index e29c6298ef..dcdb4597c5 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, 0, 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);
> > @@ -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;
>
> The offset is related with slot num, so it is better to verify the change with clustered raid.
>
> @Heming
>
>
> Thanks,
> Guoqing