--- zzzz-none-000/linux-3.10.107/Documentation/vm/transhuge.txt 2017-06-27 09:49:32.000000000 +0000 +++ scorpion-7490-727/linux-3.10.107/Documentation/vm/transhuge.txt 2021-02-04 17:41:59.000000000 +0000 @@ -120,8 +120,8 @@ It's possible to disable huge zero page by writing 0 or enable it back by writing 1: -echo 0 >/sys/kernel/mm/transparent_hugepage/khugepaged/use_zero_page -echo 1 >/sys/kernel/mm/transparent_hugepage/khugepaged/use_zero_page +echo 0 >/sys/kernel/mm/transparent_hugepage/use_zero_page +echo 1 >/sys/kernel/mm/transparent_hugepage/use_zero_page khugepaged will be automatically started when transparent_hugepage/enabled is set to "always" or "madvise, and it'll @@ -159,6 +159,27 @@ /sys/kernel/mm/transparent_hugepage/khugepaged/full_scans +max_ptes_none specifies how many extra small pages (that are +not already mapped) can be allocated when collapsing a group +of small pages into one large page. + +/sys/kernel/mm/transparent_hugepage/khugepaged/max_ptes_none + +A higher value leads to use additional memory for programs. +A lower value leads to gain less thp performance. Value of +max_ptes_none can waste cpu time very little, you can +ignore it. + +max_ptes_swap specifies how many pages can be brought in from +swap when collapsing a group of pages into a transparent huge page. + +/sys/kernel/mm/transparent_hugepage/khugepaged/max_ptes_swap + +A higher value can cause excessive swap IO and waste +memory. A lower value can prevent THPs from being +collapsed, resulting fewer pages being collapsed into +THPs, and lower memory access performance. + == Boot parameter == You can change the sysfs boot time defaults of Transparent Hugepage @@ -360,13 +381,13 @@ get_user_pages which is unacceptable as too many gup users are performance critical and they must work natively on hugepages like they work natively on hugetlbfs already (hugetlbfs is simpler because -hugetlbfs pages cannot be splitted so there wouldn't be requirement of +hugetlbfs pages cannot be split so there wouldn't be requirement of accounting the pins on the tail pages for hugetlbfs). If we wouldn't account the gup refcounts on the tail pages during gup, we won't know anymore which tail page is pinned by gup and which is not while we run split_huge_page. But we still have to add the gup pin to the head page too, to know when we can free the compound page in case it's never -splitted during its lifetime. That requires changing not just +split during its lifetime. That requires changing not just get_page, but put_page as well so that when put_page runs on a tail page (and only on a tail page) it will find its respective head page, and then it will decrease the head page refcount in addition to the