On Mon, Mar 03, 2025 at 12:00:29PM -0500, Josef Bacik wrote: > I've recently gotten annoyed with the current reference counting rules that > exist in the file system arena, specifically this pattern of having 0 referenced > objects that indicate that they're ready to be reclaimed. > > We do this everywhere, with inodes, dentries, and folios, but I specifically Folios? I don't think so. The only exceptions I know to the rule of "when a folio refcount reaches 0 it is reclaimed" are: - Frozen folios. Filesystems should never see a frozen folio. - Devmem folios. They were freed when their refcount reached 1. Alistair has that fixed in -next If there's something you don't like about the folio refcount, please let me know. I have Some Thoughts: - It's silly that the pagecache takes 2^order references on the folio. It should be just 1 - We play with the refcount in too many places. In conjunction with the first point, what I'd like is if filemap_add_folio() consumed the refcount on the folio passed to it. That is, today we allocate the folio (refcount 1), pass it to filemap_add_folio() which increments the refcount by 2^n and then put the refcount in readahead_folio(). We should do noe of that; just have the pagecacahe assume the refcount that was passed in. There are a few filesystems this would break today ... need to finish some more conversions. Anyway, what's your problem with the folio refcount? Filesystems shouldn't need to care about folio refcounts (other than fuse which decided to get all up in the mm's business).
