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Date: Mon, 11 Jan 2021 12:09:18 +0800 From: Liang Li <liliang324@...il.com> To: Mike Kravetz <mike.kravetz@...cle.com> Cc: Alexander Duyck <alexander.h.duyck@...ux.intel.com>, Mel Gorman <mgorman@...hsingularity.net>, Andrew Morton <akpm@...ux-foundation.org>, Andrea Arcangeli <aarcange@...hat.com>, Dan Williams <dan.j.williams@...el.com>, "Michael S. Tsirkin" <mst@...hat.com>, David Hildenbrand <david@...hat.com>, Jason Wang <jasowang@...hat.com>, Dave Hansen <dave.hansen@...el.com>, Michal Hocko <mhocko@...e.com>, Liang Li <liliangleo@...iglobal.com>, linux-mm <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>, virtualization@...ts.linux-foundation.org Subject: Re: [PATCH 3/6] hugetlb: add free page reporting support On Fri, Jan 8, 2021 at 6:04 AM Mike Kravetz <mike.kravetz@...cle.com> wrote: > > On 1/5/21 7:49 PM, Liang Li wrote: > > hugetlb manages its page in hstate's free page list, not in buddy > > system, this patch try to make it works for hugetlbfs. It canbe > > used for memory overcommit in virtualization and hugetlb pre zero > > out. > > I am not looking closely at the hugetlb changes yet. There seem to be > higher level questions about page reporting/etc. Once those are sorted, > I will be happy to take a closer look. One quick question below. > > > --- a/mm/hugetlb.c > > +++ b/mm/hugetlb.c > > @@ -41,6 +41,7 @@ > > #include <linux/node.h> > > #include <linux/userfaultfd_k.h> > > #include <linux/page_owner.h> > > +#include "page_reporting.h" > > #include "internal.h" > > > > int hugetlb_max_hstate __read_mostly; > > @@ -1028,6 +1029,9 @@ static void enqueue_huge_page(struct hstate *h, struct page *page) > > list_move(&page->lru, &h->hugepage_freelists[nid]); > > h->free_huge_pages++; > > h->free_huge_pages_node[nid]++; > > + if (hugepage_reported(page)) > > + __ClearPageReported(page); > > + hugepage_reporting_notify_free(h->order); > > } > > > > static struct page *dequeue_huge_page_node_exact(struct hstate *h, int nid) > > @@ -5531,6 +5535,21 @@ follow_huge_pgd(struct mm_struct *mm, unsigned long address, pgd_t *pgd, int fla > > return pte_page(*(pte_t *)pgd) + ((address & ~PGDIR_MASK) >> PAGE_SHIFT); > > } > > > > +void isolate_free_huge_page(struct page *page, struct hstate *h, int nid) > > +{ > > + VM_BUG_ON_PAGE(!PageHead(page), page); > > + > > + list_move(&page->lru, &h->hugepage_activelist); > > + set_page_refcounted(page); > > +} > > + > > +void putback_isolate_huge_page(struct hstate *h, struct page *page) > > +{ > > + int nid = page_to_nid(page); > > + > > + list_move(&page->lru, &h->hugepage_freelists[nid]); > > +} > > The above routines move pages between the free and active lists without any > update to free page counts. How does that work? Will the number of entries > on the free list get out of sync with the free_huge_pages counters? > -- > Mike Kravetz > Yes. the free_huge_pages counters will be out of sync with the free list. There are two reasons for the above code: 1. Hide the free page reporting to the user; 2. Simplify the logic to sync 'free_huge_pages' and 'resv_huge_pages'. I am not sure if it will break something else. Thanks Liang
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