On Wed, 2025-02-26 at 06:58 -0800, Christoph Hellwig wrote: > On Mon, Feb 24, 2025 at 07:33:01PM -0500, Mike Snitzer wrote: > > Add PF_KCOMPACTD flag and current_is_kcompactd() helper to check > > for > > it so nfs_release_folio() can skip calling nfs_wb_folio() from > > kcompactd. > > > > Otherwise NFS can deadlock waiting for kcompactd enduced writeback > > which recurses back to NFS (which triggers writeback to NFSD via > > NFS loopback mount on the same host, NFSD blocks waiting for XFS's > > call to __filemap_get_folio): > > Having a flag for a specific kernel thread feels wrong. I'm not an > expert in this area, but as fast as I can tell the problem is that > kcompactd should be calling into ->release_folio without __GFP_IO > set. I've had that conversation before with several mm folks before we added the PF_KSWAPD flag, and they appeared to disagree. However perhaps these daemons could set PF_MEMALLOC_NOFS before calling into release_folio()? -- Trond Myklebust Linux NFS client maintainer, Hammerspace trond.myklebust@xxxxxxxxxxxxxxx
