On 5/24/19 2:00 PM, Yang Shi wrote:
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.
By rethinking the code, I think "scan" here still should mean the number
of base pages. If the case you mentioned happens, the right behavior
should be to raise priority to give another round of scan.
And, vmscan uses sync isolation (mode = (sc->may_unmap ? 0 :
ISOLATE_UNMAPPED)), it returns -EBUSY only when the page is freed
somewhere else, so this should not cause premature OOM.
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
