| Message ID | 20200915125947.26204-6-songmuchun@bytedance.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm/hugetlb: Free some vmemmap pages of hugetlb page | expand |
On 9/15/20 5:59 AM, Muchun Song wrote: > If the size of hugetlb page is 2MB, we need 512 struct page structures > (8 pages) to be associated with it. As far as I know, we only use the > first 3 struct page structures and only read the compound_dtor members Actually, the first 4 pages can be used if CONFIG_CGROUP_HUGETLB. /* * Minimum page order trackable by hugetlb cgroup. * At least 4 pages are necessary for all the tracking information. * The second tail page (hpage[2]) is the fault usage cgroup. * The third tail page (hpage[3]) is the reservation usage cgroup. */ #define HUGETLB_CGROUP_MIN_ORDER 2 However, this still easily fits within the first page of struct page structures. > of the remaining struct page structures. For tail page, the value of > compound_dtor is the same. So we can reuse first tail page. We map the > virtual addresses of the remaining 6 tail pages to the first tail page, > and then free these 6 pages. Therefore, we need to reserve at least 2 > pages as vmemmap areas. I got confused the first time I read the above sentences. Perhaps it should be more explicit with something like: For tail pages, the value of compound_dtor is the same. So we can reuse first page of tail page structs. We map the virtual addresses of the remaining 6 pages of tail page structs to the first tail page struct, and then free these 6 pages. Therefore, we need to reserve at least 2 pages as vmemmap areas. It still does not sound great, but hopefully avoids some confusion.
On Thu, Oct 1, 2020 at 6:41 AM Mike Kravetz <mike.kravetz@oracle.com> wrote: > > On 9/15/20 5:59 AM, Muchun Song wrote: > > If the size of hugetlb page is 2MB, we need 512 struct page structures > > (8 pages) to be associated with it. As far as I know, we only use the > > first 3 struct page structures and only read the compound_dtor members > > Actually, the first 4 pages can be used if CONFIG_CGROUP_HUGETLB. Right, thanks. > /* > * Minimum page order trackable by hugetlb cgroup. > * At least 4 pages are necessary for all the tracking information. > * The second tail page (hpage[2]) is the fault usage cgroup. > * The third tail page (hpage[3]) is the reservation usage cgroup. > */ > #define HUGETLB_CGROUP_MIN_ORDER 2 > > However, this still easily fits within the first page of struct page > structures. > > > of the remaining struct page structures. For tail page, the value of > > compound_dtor is the same. So we can reuse first tail page. We map the > > virtual addresses of the remaining 6 tail pages to the first tail page, > > and then free these 6 pages. Therefore, we need to reserve at least 2 > > pages as vmemmap areas. > > I got confused the first time I read the above sentences. Perhaps it > should be more explicit with something like: > > For tail pages, the value of compound_dtor is the same. So we can reuse > first page of tail page structs. We map the virtual addresses of the > remaining 6 pages of tail page structs to the first tail page struct, > and then free these 6 pages. Therefore, we need to reserve at least 2 > pages as vmemmap areas. Sorry for my poor English. Thanks for your suggestions. I can apply this. > > It still does not sound great, but hopefully avoids some confusion. > -- > Mike Kravetz > > > So we introduce a new nr_free_vmemmap_pages field in the hstate to > > indicate how many vmemmap pages associated with a hugetlb page that we > > can free to buddy system. > > > > Signed-off-by: Muchun Song <songmuchun@bytedance.com> > > --- > > include/linux/hugetlb.h | 3 +++ > > mm/hugetlb.c | 35 +++++++++++++++++++++++++++++++++++ > > 2 files changed, 38 insertions(+) > > > > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h > > index d5cc5f802dd4..eed3dd3bd626 100644 > > --- a/include/linux/hugetlb.h > > +++ b/include/linux/hugetlb.h > > @@ -492,6 +492,9 @@ struct hstate { > > unsigned int nr_huge_pages_node[MAX_NUMNODES]; > > unsigned int free_huge_pages_node[MAX_NUMNODES]; > > unsigned int surplus_huge_pages_node[MAX_NUMNODES]; > > +#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP > > + unsigned int nr_free_vmemmap_pages; > > +#endif > > #ifdef CONFIG_CGROUP_HUGETLB > > /* cgroup control files */ > > struct cftype cgroup_files_dfl[7]; > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > > index 81a41aa080a5..f1b2b733b49b 100644 > > --- a/mm/hugetlb.c > > +++ b/mm/hugetlb.c > > @@ -1292,6 +1292,39 @@ static inline void destroy_compound_gigantic_page(struct page *page, > > unsigned int order) { } > > #endif > > > > +#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP > > +#define RESERVE_VMEMMAP_NR 2U > > + > > +static inline unsigned int nr_free_vmemmap(struct hstate *h) > > +{ > > + return h->nr_free_vmemmap_pages; > > +} > > + > > +static void __init hugetlb_vmemmap_init(struct hstate *h) > > +{ > > + unsigned int order = huge_page_order(h); > > + unsigned int vmemmap_pages; > > + > > + vmemmap_pages = ((1 << order) * sizeof(struct page)) >> PAGE_SHIFT; > > + /* > > + * The head page and the first tail page not free to buddy system, > > + * the others page will map to the first tail page. So there are > > + * (@vmemmap_pages - RESERVE_VMEMMAP_NR) pages can be freed. > > + */ > > + if (vmemmap_pages > RESERVE_VMEMMAP_NR) > > + h->nr_free_vmemmap_pages = vmemmap_pages - RESERVE_VMEMMAP_NR; > > + else > > + h->nr_free_vmemmap_pages = 0; > > + > > + pr_info("HugeTLB: can free %d vmemmap pages for %s\n", > > + h->nr_free_vmemmap_pages, h->name); > > +} > > +#else > > +static inline void hugetlb_vmemmap_init(struct hstate *h) > > +{ > > +} > > +#endif > > + > > static void update_and_free_page(struct hstate *h, struct page *page) > > { > > int i; > > @@ -3285,6 +3318,8 @@ void __init hugetlb_add_hstate(unsigned int order) > > snprintf(h->name, HSTATE_NAME_LEN, "hugepages-%lukB", > > huge_page_size(h)/1024); > > > > + hugetlb_vmemmap_init(h); > > + > > parsed_hstate = h; > > } > > > >
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index d5cc5f802dd4..eed3dd3bd626 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -492,6 +492,9 @@ struct hstate { unsigned int nr_huge_pages_node[MAX_NUMNODES]; unsigned int free_huge_pages_node[MAX_NUMNODES]; unsigned int surplus_huge_pages_node[MAX_NUMNODES]; +#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP + unsigned int nr_free_vmemmap_pages; +#endif #ifdef CONFIG_CGROUP_HUGETLB /* cgroup control files */ struct cftype cgroup_files_dfl[7]; diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 81a41aa080a5..f1b2b733b49b 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -1292,6 +1292,39 @@ static inline void destroy_compound_gigantic_page(struct page *page, unsigned int order) { } #endif +#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP +#define RESERVE_VMEMMAP_NR 2U + +static inline unsigned int nr_free_vmemmap(struct hstate *h) +{ + return h->nr_free_vmemmap_pages; +} + +static void __init hugetlb_vmemmap_init(struct hstate *h) +{ + unsigned int order = huge_page_order(h); + unsigned int vmemmap_pages; + + vmemmap_pages = ((1 << order) * sizeof(struct page)) >> PAGE_SHIFT; + /* + * The head page and the first tail page not free to buddy system, + * the others page will map to the first tail page. So there are + * (@vmemmap_pages - RESERVE_VMEMMAP_NR) pages can be freed. + */ + if (vmemmap_pages > RESERVE_VMEMMAP_NR) + h->nr_free_vmemmap_pages = vmemmap_pages - RESERVE_VMEMMAP_NR; + else + h->nr_free_vmemmap_pages = 0; + + pr_info("HugeTLB: can free %d vmemmap pages for %s\n", + h->nr_free_vmemmap_pages, h->name); +} +#else +static inline void hugetlb_vmemmap_init(struct hstate *h) +{ +} +#endif + static void update_and_free_page(struct hstate *h, struct page *page) { int i; @@ -3285,6 +3318,8 @@ void __init hugetlb_add_hstate(unsigned int order) snprintf(h->name, HSTATE_NAME_LEN, "hugepages-%lukB", huge_page_size(h)/1024); + hugetlb_vmemmap_init(h); + parsed_hstate = h; }
If the size of hugetlb page is 2MB, we need 512 struct page structures (8 pages) to be associated with it. As far as I know, we only use the first 3 struct page structures and only read the compound_dtor members of the remaining struct page structures. For tail page, the value of compound_dtor is the same. So we can reuse first tail page. We map the virtual addresses of the remaining 6 tail pages to the first tail page, and then free these 6 pages. Therefore, we need to reserve at least 2 pages as vmemmap areas. So we introduce a new nr_free_vmemmap_pages field in the hstate to indicate how many vmemmap pages associated with a hugetlb page that we can free to buddy system. Signed-off-by: Muchun Song <songmuchun@bytedance.com> --- include/linux/hugetlb.h | 3 +++ mm/hugetlb.c | 35 +++++++++++++++++++++++++++++++++++ 2 files changed, 38 insertions(+)