On Wed, Dec 20, 2023 at 9:09 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > On Thu, Dec 21, 2023 at 09:58:25AM +0800, Zhaoyang Huang wrote: > > On Wed, Dec 20, 2023 at 10:14 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > > > > > On Wed, Dec 20, 2023 at 06:29:48PM +0800, zhaoyang.huang wrote: > > > > From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx> > > > > > > > > Inactive mapped folio will be promoted to active only when it is > > > > scanned in shrink_inactive_list, while the vfs folio will do this > > > > immidiatly when it is accessed. These will introduce two affections: > > > > > > > > 1. NR_ACTIVE_FILE is not accurate as expected. > > > > 2. Low reclaiming efficiency caused by dummy nactive folio which should > > > > be kept as earlier as shrink_active_list. > > > > > > > > I would like to suggest mark the folio be accessed in minor fault to > > > > solve this situation. > > > > > > This isn't going to be as effective as you imagine. Almost all file > > > faults are handled through filemap_map_pages(). So I must ask, what > > > testing have you done with this patch? > > > > > > And while you're gathering data, what effect would this patch have on your > > > workloads? > > Thanks for heads-up, I am out of date for readahead mechanism. My goal > > It's not a terribly new mechanism ... filemap_map_pages() was added nine > years ago in 2014 by commit f1820361f83d > > > is to have mapped file pages behave like other pages which could be > > promoted immediately when they are accessed. I will update the patch > > and provide benchmark data in new patch set. > > Understood. I don't know the history of this, so I'm not sure if the > decision to not mark folios as accessed here was intentional or not. > I suspect it's entirely unintentional. It's intentional. For the active/inactive LRU, all folios start inactive. The first scan of a folio transfers the A-bit (if it's set during the initial fault) to PG_referenced; the second scan of this folio, if the A-bit is set again, moves it to the active list. This way single-use folios, i.e., folios mapped for file streaming, can be reclaimed quickly, since they are "demoted" rather than "promoted" on the second scan. This RFC would regress memory streaming workloads.
