[PATCH 00/21] erofs: patchset addressing Christoph's comments

[Christoph Hellwig]

On Mon, Sep 02, 2019 at 11:50:38PM +0800, Gao Xiang wrote:
> > > You means killing erofs_get_meta_page or avoid erofs_read_raw_page?
> > > 
> > >  - For killing erofs_get_meta_page, here is the current erofs_get_meta_page:
> > 
> > > I think it is simple enough. read_cache_page need write a similar
> > > filler, or read_cache_page_gfp will call .readpage, and then
> > > introduce buffer_heads, that is what I'd like to avoid now (no need these
> > > bd_inode buffer_heads in memory...)
> > 
> > If using read_cache_page_gfp and ->readpage works, please do.  The
> > fact that the block device inode uses buffer heads is an implementation
> > detail that might not last very long and should be invisible to you.
> > It also means you can get rid of a lot of code that you don't have
> > to maintain and others don't have to update for global API changes.
> 
> I care about those useless buffer_heads in memory for our products...
> 
> Since we are nobh filesystem (a little request, could I use it
> after buffer_heads are fully avoided, I have no idea why I need
> those buffer_heads in memory.... But I think bd_inode is good
> for caching metadata...)

Then please use read_cache_page with iomap_readpage(s), and write
comment explaining why your are not using read_cache_page_gfp.