Re: [RFC PATCH 2/8] mm: Add PG_atomic

[IBM]

Matthew Wilcox <willy@xxxxxxxxxxxxx> writes:

> On Wed, Nov 12, 2025 at 04:36:05PM +0530, Ojaswin Mujoo wrote:
>> From: John Garry <john.g.garry@xxxxxxxxxx>
>> 
>> Add page flag PG_atomic, meaning that a folio needs to be written back
>> atomically. This will be used by for handling RWF_ATOMIC buffered IO
>> in upcoming patches.
>
> Page flags are a precious resource.  I'm not thrilled about allocating one
> to this rather niche usecase.  Wouldn't this be more aptly a flag on the
> address_space rather than the folio?  ie if we're doing this kind of write
> to a file, aren't most/all of the writes to the file going to be atomic?

As of today the atomic writes functionality works on the per-write
basis (given it's a per-write characteristic). 

So, we can have two types of dirty folios sitting in the page cache of
an inode. Ones which were done using atomic buffered I/O flag
(RWF_ATOMIC) and the other ones which were non-atomic writes. Hence a
need of a folio flag to distinguish between the two writes.

-ritesh