Re: [f2fs-dev] [PATCH 0/4] f2fs: Remove uses of writepage

[Jaegeuk Kim <jaegeuk@kernel.org>]

On 03/14, Matthew Wilcox wrote:
> On Wed, Mar 12, 2025 at 01:22:41AM +0000, Jaegeuk Kim wrote:
> > On 03/12, Matthew Wilcox wrote:
> > > On Tue, Mar 11, 2025 at 07:50:38PM +0000, patchwork-bot+f2fs@kernel.org wrote:
> > > > Hello:
> > > > 
> > > > This series was applied to jaegeuk/f2fs.git (dev)
> > > > by Jaegeuk Kim <jaegeuk@kernel.org>:
> > > 
> > > Thanks!
> > > 
> > > FWIW, I have a tree with 75 patches in it on top of this that do more
> > > folio conversion work.  It's not done yet; maybe another 200 patches to
> > > go?  I don't think it's worth posting at this point in the cycle, so
> > > I'll wait until -rc1 to post, by which point it'll probably be much
> > > larger.
> > 
> > Ok, thanks for the work! Will keep an eye on.
> 
> Unfortunately, I thnk I have to abandon this effort.  It's only going
> to make supporting large folios harder (ie there would then need to be
> an equivalently disruptive series adding support for large folios).
> 
> The fundamental problem is that f2fs has no concept of block size !=
> PAGE_SIZE.  So if you create a filesystem on a 4kB PAGE_SIZE kernel,
> you can't mount it on a 16kB PAGE_SIZE kernel.  An example:
> 
> int f2fs_recover_inline_xattr(struct inode *inode, struct page *page)
> {
>         struct f2fs_inode *ri;
>         ipage = f2fs_get_node_page(F2FS_I_SB(inode), inode->i_ino);
>         ri = F2FS_INODE(page);
> 
> so an inode number is an index into the filesystem in PAGE_SIZE units,
> not in filesystem block size units.  Fixing this is a major effort, and
> I lack the confidence in my abilities to do it without breaking anything.
> 
> As an outline of what needs to happen, I think that rather than passing
> around so many struct page pointers, we should be passing around either
> folio + offset, or we should be passing around struct f2fs_inode pointers.
> My preference is for the latter.  We can always convert back to the
> folio containing the inode if we need to (eg to mark it dirty) and it
> adds some typesafety by ensuring that we're passing around pointers that
> we believe belong to an inode and not, say, a struct page which happens
> to contain a directory entry.
> 
> This is a monster task, I think.  I'm going to have to disable f2fs
> from testing with split page/folio.  This is going to be a big problem
> for Android.

I see. fyi; in Android, I'm thinking to run 16KB page kernel with 16KB format
natively to keep block_size = PAGE_SIZE. Wasn't large folio to support a set
of pages while keeping block_size = PAGE_SIZE?