Re: [PATCH v1 07/14] fs: Add aop_flags parameter to create_page_buffers()

Stefan Roesch
2022-02-16T18:31:01Z

On 2/14/22 10:14 AM, Matthew Wilcox wrote:
> On Mon, Feb 14, 2022 at 09:43:56AM -0800, Stefan Roesch wrote:
>> This adds the aop_flags parameter to the create_page_buffers function.
>> When AOP_FLAGS_NOWAIT parameter is set, the atomic allocation flag is
>> set. The AOP_FLAGS_NOWAIT flag is set, when async buffered writes are
>> enabled.
>
> Why is this better than passing in gfp flags directly?
>

I don't think that gfp flags are a great fit here. We only want to pass in
a nowait flag and this does not map nicely to a gfp flag.

Instead of passing in a flag parameter we can also pass in a bool parameter,
however that has its limitations as it can't be extended in the future.

>> Signed-off-by: Stefan Roesch <shr@fb.com>
>> ---
>> fs/buffer.c | 28 +++++++++++++++++++++-------
>> 1 file changed, 21 insertions(+), 7 deletions(-)
>>
>> diff --git a/fs/buffer.c b/fs/buffer.c
>> index 948505480b43..5e3067173580 100644
>> --- a/fs/buffer.c
>> +++ b/fs/buffer.c
>> @@ -1682,13 +1682,27 @@ static inline int block_size_bits(unsigned int blocksize)
>> return ilog2(blocksize);
>> }
>>
>> -static struct buffer_head *create_page_buffers(struct page *page, struct inode *inode, unsigned int b_state)
>> +static struct buffer_head *create_page_buffers(struct page *page,
>> + struct inode *inode,
>> + unsigned int b_state,
>> + unsigned int aop_flags)
>> {
>> BUG_ON(!PageLocked(page));
>>
>> - if (!page_has_buffers(page))
>> - create_empty_buffers(page, 1 << READ_ONCE(inode->i_blkbits),
>> - b_state);
>> + if (!page_has_buffers(page)) {
>> + gfp_t gfp = GFP_NOFS | __GFP_ACCOUNT;
>> +
>> + if (aop_flags & AOP_FLAGS_NOWAIT) {
>> + gfp |= GFP_ATOMIC | __GFP_NOWARN;
>> + gfp &= ~__GFP_DIRECT_RECLAIM;
>> + } else {
>> + gfp |= __GFP_NOFAIL;
>> + }
>> +
>> + __create_empty_buffers(page, 1 << READ_ONCE(inode->i_blkbits),
>> + b_state, gfp);
>> + }
>> +
>> return page_buffers(page);
>> }
>>
>> @@ -1734,7 +1748,7 @@ int __block_write_full_page(struct inode *inode, struct page *page,
>> int write_flags = wbc_to_write_flags(wbc);
>>
>> head = create_page_buffers(page, inode,
>> - (1 << BH_Dirty)|(1 << BH_Uptodate));
>> + (1 << BH_Dirty)|(1 << BH_Uptodate), 0);
>>
>> /*
>> * Be very careful. We have no exclusion from __set_page_dirty_buffers
>> @@ -2000,7 +2014,7 @@ int __block_write_begin_int(struct folio *folio, loff_t pos, unsigned len,
>> BUG_ON(to > PAGE_SIZE);
>> BUG_ON(from > to);
>>
>> - head = create_page_buffers(&folio->page, inode, 0);
>> + head = create_page_buffers(&folio->page, inode, 0, flags);
>> blocksize = head->b_size;
>> bbits = block_size_bits(blocksize);
>>
>> @@ -2280,7 +2294,7 @@ int block_read_full_page(struct page *page, get_block_t *get_block)
>> int nr, i;
>> int fully_mapped = 1;
>>
>> - head = create_page_buffers(page, inode, 0);
>> + head = create_page_buffers(page, inode, 0, 0);
>> blocksize = head->b_size;
>> bbits = block_size_bits(blocksize);
>>
>> --
>> 2.30.2
>>