Messages in this thread | | | Subject | Re: [v4 PATCH 2/2] mm: vmscan: correct some vmscan counters for | From | Yang Shi <> | Date | Fri, 24 May 2019 14:00:00 +0800 |
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On 5/24/19 1:51 PM, Hillf Danton wrote: > On Fri, 24 May 2019 09:27:02 +0800 Yang Shi wrote: >> On 5/23/19 11:51 PM, Hillf Danton wrote: >>> On Thu, 23 May 2019 10:27:38 +0800 Yang Shi wrote: >>>> @ -1642,14 +1650,14 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan, >>>> unsigned long nr_zone_taken[MAX_NR_ZONES] = { 0 }; >>>> unsigned long nr_skipped[MAX_NR_ZONES] = { 0, }; >>>> unsigned long skipped = 0; >>>> - unsigned long scan, total_scan, nr_pages; >>>> + unsigned long scan, total_scan; >>>> + unsigned long nr_pages; >>> Change for no earn:) >> Aha, yes. >> >>>> LIST_HEAD(pages_skipped); >>>> isolate_mode_t mode = (sc->may_unmap ? 0 : ISOLATE_UNMAPPED); >>>> + total_scan = 0; >>>> scan = 0; >>>> - for (total_scan = 0; >>>> - scan < nr_to_scan && nr_taken < nr_to_scan && !list_empty(src); >>>> - total_scan++) { >>>> + while (scan < nr_to_scan && !list_empty(src)) { >>>> struct page *page; >>> AFAICS scan currently prevents us from looping for ever, while nr_taken bails >>> us out once we get what's expected, so I doubt it makes much sense to cut >>> nr_taken off. >> It is because "scan < nr_to_scan && nr_taken >= nr_to_scan" is >> impossible now with the units fixed. >> > With the units fixed, nr_taken is no longer checked.
It is because scan would be always >= nr_taken.
> >>>> page = lru_to_page(src); >>>> @@ -1657,9 +1665,12 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan, >>>> VM_BUG_ON_PAGE(!PageLRU(page), page); >>>> + nr_pages = 1 << compound_order(page); >>>> + total_scan += nr_pages; >>>> + >>>> if (page_zonenum(page) > sc->reclaim_idx) { >>>> list_move(&page->lru, &pages_skipped); >>>> - nr_skipped[page_zonenum(page)]++; >>>> + nr_skipped[page_zonenum(page)] += nr_pages; >>>> continue; >>>> } >>>> @@ -1669,10 +1680,9 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan, >>>> * ineligible pages. This causes the VM to not reclaim any >>>> * pages, triggering a premature OOM. >>>> */ >>>> - scan++; >>>> + scan += nr_pages; >>> The comment looks to defy the change if we fail to add a huge page to >>> the dst list; otherwise nr_taken knows how to do the right thing. What >>> I prefer is to let scan to do one thing a time. >> I don't get your point. Do you mean the comment "Do not count skipped >> pages because that makes the function return with no isolated pages if >> the LRU mostly contains ineligible pages."? I'm supposed the comment is >> used to explain why not count skipped page. >> > Well consider the case where there is a huge page in the second place > reversely on the src list along with other 20 regular pages, and we are > not able to add the huge page to the dst list. Currently we can go on and > try to scan other pages, provided nr_to_scan is 32; with the units fixed, > however, scan goes over nr_to_scan, leaving us no chance to scan any page > that may be not busy. I wonder that triggers a premature OOM, because I > think scan means the number of list nodes we try to isolate, and > nr_taken the number of regular pages successfully isolated.
Yes, good point. I think I just need roll back to what v3 did here to get scan accounted for each case separately to avoid the possible over-account.
>>>> switch (__isolate_lru_page(page, mode)) { >>>> case 0: >>>> - nr_pages = hpage_nr_pages(page); >>>> nr_taken += nr_pages; >>>> nr_zone_taken[page_zonenum(page)] += nr_pages; >>>> list_move(&page->lru, dst); >>>> -- >>>> 1.8.3.1 > Best Regards > Hillf
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