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Date:   Thu, 14 Oct 2021 16:58:46 +0800
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Subject: Re: [PATCH 4/5] md: Kill usage of page->index
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To:     Guoqing Jiang <guoqing.jiang@linux.dev>,
        Kent Overstreet <kent.overstreet@gmail.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        akpm@linux-foundation.org, linux-raid@vger.kernel.org,
        linux-block@vger.kernel.org, axboe@kernel.dk
CC:     alexander.h.duyck@linux.intel.com
References: <20211013160034.3472923-1-kent.overstreet@gmail.com>
 <20211013160034.3472923-5-kent.overstreet@gmail.com>
 <bcdd4b56-9b6b-c5cb-2eb7-540fa003d692@linux.dev>
From:   "heming.zhao@suse.com" <heming.zhao@suse.com>
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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 bit=
map.

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

Thanks,
Heming

On 10/14/21 16:02, Guoqing Jiang wrote:
>=20
>=20
> 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@gmail.com>
>> ---
>> =C2=A0 drivers/md/md-bitmap.c | 44 ++++++++++++++++++++-----------------=
-----
>> =C2=A0 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,
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (sync_page_io(=
rdev, target,
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 roundup(size, bdev_logical_block_size(=
rdev->bdev)),
>> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0 page, REQ_OP_READ, 0, true)) {
>> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 page=
->index =3D index;
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0 page, REQ_OP_READ, 0, true))
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0 return 0;
>> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 }
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 }
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 return -EIO;
>> =C2=A0 }
>> @@ -209,7 +207,8 @@ static struct md_rdev *next_active_rdev(struct md_rd=
ev *rdev, struct mddev *mdde
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 return NULL;
>> =C2=A0 }
>> -static int write_sb_page(struct bitmap *bitmap, struct page *page, int =
wait)
>> +static int write_sb_page(struct bitmap *bitmap, struct page *page,
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0 unsigned long index, int wait)
>> =C2=A0 {
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 struct md_rdev *rdev;
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 struct block_device *bdev;
>> @@ -224,7 +223,7 @@ static int write_sb_page(struct bitmap *bitmap, stru=
ct page *page, int wait)
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 bdev =3D (rdev->m=
eta_bdev) ? rdev->meta_bdev : rdev->bdev;
>> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (page->index =3D=3D store=
->file_pages-1) {
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (index =3D=3D store->file=
_pages-1) {
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0 int last_page_size =3D store->bytes & (PAGE_SIZE-1);
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0 if (last_page_size =3D=3D 0)
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 last_page_size =3D PAGE_SIZE;
>> @@ -236,8 +235,7 @@ static int write_sb_page(struct bitmap *bitmap, stru=
ct page *page, int wait)
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 */
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (mddev->extern=
al) {
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0 /* Bitmap could be anywhere. */
>> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (=
rdev->sb_start + offset + (page->index
>> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 * (PAGE_SIZE/512))
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (=
rdev->sb_start + offset + index * PAGE_SECTORS
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 > rdev->data_offset
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 &&
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 rdev->sb_start + offset
>> @@ -247,7 +245,7 @@ static int write_sb_page(struct bitmap *bitmap, stru=
ct page *page, int wait)
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } else if (offset=
 < 0) {
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0 /* DATA=C2=A0 BITMAP METADATA=C2=A0 */
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0 if (offset
>> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0 + (long)(page->index * (PAGE_SIZE/512))
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0 + (long)(index * PAGE_SECTORS)
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 + size/512 > 0)
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /* bitmap runs in to metadata */
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 goto bad_alignment;
>> @@ -259,7 +257,7 @@ static int write_sb_page(struct bitmap *bitmap, stru=
ct page *page, int wait)
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0 /* METADATA BITMAP DATA */
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0 if (rdev->sb_start
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 + offset
>> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0 + page->index*(PAGE_SIZE/512) + size/512
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0 + index * PAGE_SECTORS + size/512
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 > rdev->data_offset)
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /* bitmap runs in to data */
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 goto bad_alignment;
>> @@ -268,7 +266,7 @@ static int write_sb_page(struct bitmap *bitmap, stru=
ct page *page, int wait)
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 }
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 md_super_write(md=
dev, rdev,
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 rdev->sb_start + offset
>> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 + page->index * (PAGE_SIZE/512),
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 + index * PAGE_SECTORS,
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 size,
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 page);
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 }
>> @@ -285,12 +283,13 @@ static void md_bitmap_file_kick(struct bitmap *bit=
map);
>> =C2=A0 /*
>> =C2=A0=C2=A0 * write out a page to a file
>> =C2=A0=C2=A0 */
>> -static void write_page(struct bitmap *bitmap, struct page *page, int wa=
it)
>> +static void write_page(struct bitmap *bitmap, struct page *page,
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0 unsigned long index, int wait)
>> =C2=A0 {
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 struct buffer_head *bh;
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (bitmap->storage.file =3D=3D NULL) {
>> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 switch (write_sb_page(bitmap=
, page, wait)) {
>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 switch (write_sb_page(bitmap=
, page, index, wait)) {
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 case -EINVAL:
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0 set_bit(BITMAP_WRITE_ERROR, &bitmap->flags);
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 }
>> @@ -399,7 +398,6 @@ static int read_page(struct file *file, unsigned lon=
g index,
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 blk_cur++;
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 bh =3D bh->b_this=
_page;
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 }
>> -=C2=A0=C2=A0=C2=A0 page->index =3D index;
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 wait_event(bitmap->write_wait,
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
 atomic_read(&bitmap->pending_writes)=3D=3D0);
>> @@ -472,7 +470,7 @@ void md_bitmap_update_sb(struct bitmap *bitmap)
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 sb->sectors_reserved =3D cpu_to_le32(bitm=
ap->mddev->
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 bi=
tmap_info.space);
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 kunmap_atomic(sb);
>> -=C2=A0=C2=A0=C2=A0 write_page(bitmap, bitmap->storage.sb_page, 1);
>> +=C2=A0=C2=A0=C2=A0 write_page(bitmap, bitmap->storage.sb_page, 0, 1);
>> =C2=A0 }
>> =C2=A0 EXPORT_SYMBOL(md_bitmap_update_sb);
>> @@ -524,7 +522,6 @@ static int md_bitmap_new_disk_sb(struct bitmap *bitm=
ap)
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 bitmap->storage.sb_page =3D alloc_page(GF=
P_KERNEL | __GFP_ZERO);
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (bitmap->storage.sb_page =3D=3D NULL)
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 return -ENOMEM;
>> -=C2=A0=C2=A0=C2=A0 bitmap->storage.sb_page->index =3D 0;
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 sb =3D kmap_atomic(bitmap->storage.sb_pag=
e);
>> @@ -802,7 +799,6 @@ static int md_bitmap_storage_alloc(struct bitmap_sto=
rage *store,
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (store->sb_page) {
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 store->filemap[0]=
 =3D store->sb_page;
>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 pnum =3D 1;
>> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 store->sb_page->index =3D of=
fset;
>=20
> The offset is related with slot num, so it is better to verify the change=
 with clustered raid.
>=20
> @Heming
>=20
>=20
> Thanks,
> Guoqing
>=20