Re: [RFC PATCH 34/40] btrfs: allocate eb-attached btree pages as movable

[David Sterba <dsterba@suse.cz>]

On Wed, May 20, 2026 at 10:47:49AM -0700, Boris Burkov wrote:
> > @@ -689,14 +704,23 @@ int btrfs_alloc_page_array(unsigned int nr_pages, struct page **page_array,
> >   * Populate needed folios for the extent buffer.
> >   *
> >   * For now, the folios populated are always in order 0 (aka, single page).
> > + *
> > + * @movable: pass true only when the resulting pages will be attached to
> > + *           btree_inode->i_mapping (the alloc_extent_buffer real path).
> > + *           Cloned/dummy extent buffers (EXTENT_BUFFER_UNMAPPED) leave
> > + *           folio->mapping NULL, never enter the LRU, and never get the
> > + *           btree_migrate_folio aops, so __GFP_MOVABLE would violate the
> > + *           page-allocator's migrability contract for them.
> >   */
> 
> My gut says it is nicer to just transparently pass along a gfp flag
> rather than a carefully documented movable boolean and let the callers
> do the right thing. Just a nit, I don't care strongly about it.

Agreed, the GFP flags would be better and also a bit more self
documenting where the functions are called. The patch is not standalone
so I don't mind having the booleans, we can clean it up later to let the
40-patch series proceed.