On Mon, Jan 31, 2022 at 03:03:53PM +1100, NeilBrown wrote: > - .writepage to return AOP_WRITEPAGE_ACTIVATE if WB_SYNC_NONE > and the flag is set. Is this actually useful? I ask because Dave Chinner believes the call to ->writepage in vmscan to be essentially unused. See commit 21b4ee7029c9, and I had a followup discussion with him on IRC: <willy> dchinner: did you gather any stats on how often ->writepage was being called by pageout() before "xfs: drop ->writepage completely" was added? <dchinner> willy: Never saw it on XFS in 3 years in my test environment... <dchinner> I don't ever recall seeing the memory reclaim guards we put on ->writepage in XFS ever firing - IIRC they'd been there for the best part of a decade. <willy> not so much the WARN_ON firing but the case where it actually calls iomap_writepage <dchinner> willy: I mean both - I was running with a local patch that warned on writepage for a long time, regardless of where it was called from. I can believe things are different for a network filesystem, or maybe XFS does background writeback better than other filesystems, but it would be intriguing to be able to get rid of ->writepage altogether (or at least from pageout(); migrate.c may be a thornier proposition).
