On Wed, Feb 09, 2022 at 03:54:10PM -0600, Goldwyn Rodrigues wrote: > Copy-on-write filesystem such as btrfs (or reflinks in XFS/OCFS2) have > files which share extents on disk. Multiple files can have extents > pointing to same physical disk location. When mutliple files share a > common extent and these files are read(), each file will have it's own > copy of the content in the page cache. > > The problem is this leads to wastage of memory since multiple > copies of the same content is in memory. The proposal is to have a > common cache which would be used *for reads only* (excluding read before > writes for non page aligned writes). > > I would like to discuss the problems which will arise to implement this: > - strategies to maintain such a shared cache > - location of the shared cache: device inode or separate inode? > - all reads go through shared cache OR only shared extents > should be in shared cache > - actions to perform if write occurs at offsets of shared extents > - should it be CoW'd in memory? OR > - move the pages from shared cache to inode's cache? > - what should be done to the pages after writeback. Should they be > dropped, so further reads are read into shared cache? > - Shrinking in case of system memory pressure > > An initial RFC patch was posted here: > https://lore.kernel.org/all/YXNoxZqKPkxZvr3E@xxxxxxxxxxxxxxxxxxxx/t/ Yes, we should discuss this. Sorry I've been too busy to work on it recently. Hopefully I have time this year.
