Re: [PATCH 2/8] staging: erofs: separate erofs_get_meta_page

Chao Yu
2018-08-13T12:34:40Z

On 2018/8/13 19:04, Dan Carpenter wrote:
> On Sun, Aug 12, 2018 at 10:01:44PM +0800, Chao Yu wrote:
>> --- a/drivers/staging/erofs/data.c
>> +++ b/drivers/staging/erofs/data.c
>> @@ -39,31 +39,44 @@ static inline void read_endio(struct bio *bio)
>> }
>>
>> /* prio -- true is used for dir */
>> -struct page *erofs_get_meta_page(struct super_block *sb,
>> - erofs_blk_t blkaddr, bool prio)
>> +struct page *__erofs_get_meta_page(struct super_block *sb,
>> + erofs_blk_t blkaddr, bool prio, bool nofail)
>> {
>> - struct inode *bd_inode = sb->s_bdev->bd_inode;
>> - struct address_space *mapping = bd_inode->i_mapping;
>> + struct inode *const bd_inode = sb->s_bdev->bd_inode;
>> + struct address_space *const mapping = bd_inode->i_mapping;
>> + /* prefer retrying in the allocator to blindly looping below */
>> + const gfp_t gfp = mapping_gfp_constraint(mapping, ~__GFP_FS) |
>> + (nofail ? __GFP_NOFAIL : 0);
>> + unsigned int io_retries = nofail ? EROFS_IO_MAX_RETRIES_NOFAIL : 0;
>> struct page *page;
>>
>> repeat:
>> - page = find_or_create_page(mapping, blkaddr,
>> - /*
>> - * Prefer looping in the allocator rather than here,
>> - * at least that code knows what it's doing.
>> - */
>> - mapping_gfp_constraint(mapping, ~__GFP_FS) | __GFP_NOFAIL);
>> -
>> - BUG_ON(!page || !PageLocked(page));
>> + page = find_or_create_page(mapping, blkaddr, gfp);
>> + if (unlikely(page == NULL)) {
>> + DBG_BUGON(nofail);
>> + return ERR_PTR(-ENOMEM);
>> + }
>> + DBG_BUGON(!PageLocked(page));
>>
>> if (!PageUptodate(page)) {
>> struct bio *bio;
>> int err;
>>
>> - bio = erofs_grab_bio(sb, blkaddr, 1, read_endio, true);
>> + bio = erofs_grab_bio(sb, blkaddr, 1, read_endio, nofail);
>> + if (unlikely(bio == NULL)) {
>> + DBG_BUGON(nofail);
>> + err = -ENOMEM;
>> +err_out:
>> + unlock_page(page);
>> + put_page(page);
>> + return ERR_PTR(err);
>
>
> Put this err_out stuff at the bottom of the function so that we don't
> have to do backward hops to get to it.

Agreed, we can move error path at the bottom of this function.

>
>> + }
>>
>> err = bio_add_page(bio, page, PAGE_SIZE, 0);
>> - BUG_ON(err != PAGE_SIZE);
>> + if (unlikely(err != PAGE_SIZE)) {
>> + err = -EFAULT;
>> + goto err_out;
> ^^^^^^^^^^^^
> Like this. Generally avoid backwards hops if you can.
>
>> + }
>>
>> __submit_bio(bio, REQ_OP_READ,
>> REQ_META | (prio ? REQ_PRIO : 0));
>> @@ -72,6 +85,7 @@ struct page *erofs_get_meta_page(struct super_block *sb,
>>
>> /* the page has been truncated by others? */
>> if (unlikely(page->mapping != mapping)) {
>> +unlock_repeat:
>
> The question mark in the "truncated by others?" is a little concerning.

Yup, we can remove the question mark.

> It's slightly weird that we don't check "io_retries" on this path.

We don't need to cover this path since io_retries is used for accounting retry
time only when IO occurs.

Thanks,

>
>> unlock_page(page);
>> put_page(page);
>> goto repeat;
>> @@ -79,10 +93,12 @@ struct page *erofs_get_meta_page(struct super_block *sb,
>>
>> /* more likely a read error */
>> if (unlikely(!PageUptodate(page))) {
>> - unlock_page(page);
>> - put_page(page);
>> -
>> - page = ERR_PTR(-EIO);
>> + if (io_retries) {
>> + --io_retries;
>> + goto unlock_repeat;
>> + }
>> + err = -EIO;
>> + goto err_out;
>
> regards,
> dan carpenter
>