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Date: Thu, 18 Mar 2021 10:59:10 +0100
From: Oscar Salvador <osalvador@...e.de>
To: Michal Hocko <mhocko@...e.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Vlastimil Babka <vbabka@...e.cz>,
David Hildenbrand <david@...hat.com>,
Muchun Song <songmuchun@...edance.com>,
Mike Kravetz <mike.kravetz@...cle.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 4/5] mm: Make alloc_contig_range handle in-use hugetlb
pages
On Thu, Mar 18, 2021 at 10:29:57AM +0100, Michal Hocko wrote:
> On Thu 18-03-21 09:54:01, Oscar Salvador wrote:
> [...]
> > @@ -2287,10 +2288,12 @@ static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page)
> > goto unlock;
> > } else if (page_count(old_page)) {
> > /*
> > - * Someone has grabbed the page, fail for now.
> > + * Someone has grabbed the page, try to isolate it here.
> > + * Fail with -EBUSY if not possible.
> > */
> > - ret = -EBUSY;
> > update_and_free_page(h, new_page);
> > + if (!isolate_huge_page(old_page, list)
> > + ret = -EBUSY;
> > goto unlock;
> > } else if (!HPageFreed(old_page)) {
>
> I do not think you want to call isolate_huge_page with hugetlb_lock
> held. You would need to drop the lock before calling isolate_huge_page.
Yeah, that was an oversight. As I said I did not compile it(let alone
test it), otherwise the system would have screamed I guess.
I was more interested in knowing whether how did it look wrt. retry
concerns:
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index bcff86ca616f..a37b4ce86e58 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -583,7 +583,7 @@ struct huge_bootmem_page {
struct hstate *hstate;
};
-int isolate_or_dissolve_huge_page(struct page *page);
+int isolate_or_dissolve_huge_page(struct page *page, struct list_head *list);
struct page *alloc_huge_page(struct vm_area_struct *vma,
unsigned long addr, int avoid_reserve);
struct page *alloc_huge_page_nodemask(struct hstate *h, int preferred_nid,
@@ -866,7 +866,8 @@ static inline void huge_ptep_modify_prot_commit(struct vm_area_struct *vma,
#else /* CONFIG_HUGETLB_PAGE */
struct hstate {};
-static inline int isolate_or_dissolve_huge_page(struct page *page)
+static inline int isolate_or_dissolve_huge_page(struct page *page,
+ struct list_head *list)
{
return -ENOMEM;
}
diff --git a/mm/compaction.c b/mm/compaction.c
index 9f253fc3b4f9..6e47855fd154 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -910,7 +910,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
}
if (PageHuge(page) && cc->alloc_contig) {
- ret = isolate_or_dissolve_huge_page(page);
+ ret = isolate_or_dissolve_huge_page(page, &cc->migratepages);
/*
* Fail isolation in case isolate_or_dissolve_huge_page
@@ -927,6 +927,15 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
goto isolate_fail;
}
+ if (PageHuge(page)) {
+ /*
+ * Hugepage was successfully isolated and placed
+ * on the cc->migratepages list.
+ */
+ low_pfn += compound_nr(page) - 1;
+ goto isolate_success_no_list;
+ }
+
/*
* Ok, the hugepage was dissolved. Now these pages are
* Buddy and cannot be re-allocated because they are
@@ -1068,6 +1077,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
isolate_success:
list_add(&page->lru, &cc->migratepages);
+isolate_success_no_list:
cc->nr_migratepages += compound_nr(page);
nr_isolated += compound_nr(page);
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 3194c1bd9e32..f55fa6acc6f9 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2257,7 +2257,8 @@ static void restore_reserve_on_error(struct hstate *h,
* Returns 0 on success, otherwise negated error.
*/
-static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page)
+static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page,
+ struct list_head *list)
{
gfp_t gfp_mask = htlb_alloc_mask(h) | __GFP_THISNODE;
int nid = page_to_nid(old_page);
@@ -2287,10 +2288,14 @@ static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page)
goto unlock;
} else if (page_count(old_page)) {
/*
- * Someone has grabbed the page, fail for now.
+ * Someone has grabbed the page, try to isolate it here.
+ * Fail with -EBUSY if not possible.
*/
- ret = -EBUSY;
update_and_free_page(h, new_page);
+ spin_unlock(&hugetlb_lock);
+ if (!isolate_huge_page(old_page, list)
+ ret = -EBUSY;
+ spin_lock(&hugetlb_lock);
goto unlock;
} else if (!HPageFreed(old_page)) {
/*
@@ -2319,10 +2324,11 @@ static int alloc_and_dissolve_huge_page(struct hstate *h, struct page *old_page)
return ret;
}
-int isolate_or_dissolve_huge_page(struct page *page)
+int isolate_or_dissolve_huge_page(struct page *page, struct list_head *list)
{
struct hstate *h;
struct page *head;
+ int ret = -EBUSY;
/*
* The page might have been dissolved from under our feet, so make sure
@@ -2347,7 +2353,12 @@ int isolate_or_dissolve_huge_page(struct page *page)
if (hstate_is_gigantic(h))
return -ENOMEM;
- return alloc_and_dissolve_huge_page(h, head);
+ if (page_count(head) && isolate_huge_page(head, list))
+ ret = 0;
+ else if (!page_count(head))
+ ret = alloc_and_dissolve_huge_page(h, head, list);
+
+ return ret;
}
struct page *alloc_huge_page(struct vm_area_struct *vma,
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 562e87cbd7a1..42aaef30633e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1507,8 +1507,9 @@ unsigned int reclaim_clean_pages_from_list(struct zone *zone,
LIST_HEAD(clean_pages);
list_for_each_entry_safe(page, next, page_list, lru) {
- if (page_is_file_lru(page) && !PageDirty(page) &&
- !__PageMovable(page) && !PageUnevictable(page)) {
+ if (!PageHuge(page) && page_is_file_lru(page) &&
+ !PageDirty(page) && !__PageMovable(page) &&
+ !PageUnevictable(page)) {
ClearPageActive(page);
list_move(&page->lru, &clean_pages);
}
The spin_lock after the isolate_huge_page() in
alloc_and_dissolve_huge_page() could probably be spared by placing a
goto out directly before the return.
But just a POC.
--
Oscar Salvador
SUSE L3
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