On Wed, Jun 28, 2023 at 04:19:01PM +0530, Charan Teja Kalla wrote: > Hi Pavan, > > On 6/27/2023 7:26 PM, Pavan Kondeti wrote: > >> A folio turns into a Workingset during: > >> 1) shrink_active_list() placing the folio from active to inactive list. > >> 2) When a workingset transition is happening during the folio refault. > >> > >> And when Workingset is set on a folio, PSI for memory can be accounted > >> during a) That folio is being reclaimed and b) Refault of that folio. > >> > > Please help me understand why PSI for memory (I understood it as the > > time spent in psi_memstall_enter() to psi_memstall_leave()) would be > > accounted in (a) i.e during reclaim. I understand that when a working > > > > The (b) part is very clear. > > > I meant to say, for usual reclaim, PSI is accounted on a folio for both > reclaim and as well during the refault operation when Workingset is set > on a folio i.e., both a) and b) cases above. > Got it. > >> This accounting of PSI for memory is not consistent in the cases where > >> clients use madvise(COLD/PAGEOUT) to deactivate or proactively reclaim a > >> folio: > > Seems I need to be explicit here. How about the below? > > This accounting of PSI for memory is not consistent for reclaim + > refault operation between usual reclaim and madvise(COLD/PAGEOUT) which > deactivate or proactively reclaim a folio: > Looks good. > lmk for any better rephrasing? > >> a) A folio started at inactive and moved to active as part of accesses. > >> Workingset is absent on the folio thus madvise(MADV_PAGEOUT) don't > >> account such folios for PSI. > >> > >> b) When the same folio transition from inactive->active and then to > >> inactive through shrink_active_list(). Workingset is set on the folio > >> thus madvise(MADV_PAGEOUT) account such folios for PSI. > >> > >> c) When the same folio is part of active list directly as a result of > >> folio refault and this was a workingset folio prior to eviction. > >> Workingset is set on the folio thus both the operations of MADV_PAGEOUT > >> and reclaim of the MADV_COLD operated folio account for PSI. > >> > >> d) madvise(MADV_COLD) transfers the folio from active list to inactive > >> list. Such folios may not have the Workingset thus reclaim operation > >> on such folio doesn't account for PSI. > > This is not limited to madvise(PAGEOUT) right, anywhere an active page > > is reclaimed we have the same problem. For ex: damon_pa_pageout() and > > __alloc_contig_migrate_range()->reclaim_clean_pages_from_list(). > >> If that is the case, can we set mark a folio as a workingset when it is > > activated? That way, we don't have make madvise() as a special case? > I think marking the folio as a workingset when it sits on the active is > not a correct thing. For the same example you mentioned, a simple CMA > allocation will be dropping the clean pages instead of migration. PSI > accounting on refault of those pages don't reveal anything to the user. > Agreed. Thanks for the clarification. > Where as in the madvise() cases, this PSI tells the user about the type > of pages that he is working on.[1] > > BTW, damon_pa_pageout() seems a valid case above. let me fix it in the > next patch. Looks good. Thanks, Pavan
