On Mon, Nov 11, 2024 at 09:35:09AM +0800, Huang, Ying wrote: > Gregory Price <gourry@xxxxxxxxxx> writes: > > > > > Exploring and testing this a little further, I brought this up to current > > folio work in 6.9 and found this solution to be unstable as-is. > > > > After some work to fix lock/reference issues, Johannes pointed out that > > __filemap_get_folio can be called from an atomic context - which means it > > may not be safe to do migrations in this context. > > Sorry, I don't understand this, the above patch changes > filemap_get_pages() and grab_cache_page_write_begin() instead of > __filemap_get_folio(). > on newer kernels, grab_cache_page_write_begin is a compat wrapper for __filemap_get_folio and folio_file_page. This chunk of code has changed somewhat significantly, actually. > > We're back to looking at something like an LRU-esque system, but now we're > > thinking about isolating the folios in folio_mark_accessed into a task-local > > list, and then process the list on resume. > > If necessary, we can use a similar method for above solution too. And > we can filter accessed once folios with folio_mark_accessed() firstly. > That is, only promote a page if, > > - record the folio access time in folio_mark_accessed() only > - when the folio are accessed again, and "access_time - record_time < > threshold", promote the folio. > yes this was the thought. > > Basically we're thinking > > > > 1) hook folio_mark_accessed and use PG_ACTIVE/PG_ACCESSED to determine whether > > the page is a promotion candidate. > > 2) if it is, isolate it from the LRU - which is safe because folio_mark_accessed > > already does this elsewhere, and place it onto current->promo_queue > > 3) set_notify_resume > > 4) add logic to resume_user_mode_work() to run through current->promo_queue and > > either promote the pages accordingly, or do folio_putback_lru on failure. > > Use a task_work? > probably more correct, had a discussion about kernel threads accessing file cache and we weren't sure if that situation even existed - so probably going to try task_work first. ~Gregory
