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Message-ID: <219bd2d0-92ef-bcac-458a-0df6190fa387@redhat.com>
Date: Tue, 19 Apr 2022 18:46:43 +0200
From: David Hildenbrand <david@...hat.com>
To: Vlastimil Babka <vbabka@...e.cz>, linux-kernel@...r.kernel.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Hugh Dickins <hughd@...gle.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
David Rientjes <rientjes@...gle.com>,
Shakeel Butt <shakeelb@...gle.com>,
John Hubbard <jhubbard@...dia.com>,
Jason Gunthorpe <jgg@...dia.com>,
Mike Kravetz <mike.kravetz@...cle.com>,
Mike Rapoport <rppt@...ux.ibm.com>,
Yang Shi <shy828301@...il.com>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
Matthew Wilcox <willy@...radead.org>,
Jann Horn <jannh@...gle.com>, Michal Hocko <mhocko@...nel.org>,
Nadav Amit <namit@...are.com>, Rik van Riel <riel@...riel.com>,
Roman Gushchin <guro@...com>,
Andrea Arcangeli <aarcange@...hat.com>,
Peter Xu <peterx@...hat.com>,
Donald Dutile <ddutile@...hat.com>,
Christoph Hellwig <hch@....de>,
Oleg Nesterov <oleg@...hat.com>, Jan Kara <jack@...e.cz>,
Liang Zhang <zhangliang5@...wei.com>,
Pedro Gomes <pedrodemargomes@...il.com>,
Oded Gabbay <oded.gabbay@...il.com>, linux-mm@...ck.org
Subject: Re: [PATCH v3 12/16] mm: remember exclusively mapped anonymous pages
with PG_anon_exclusive
On 13.04.22 20:28, Vlastimil Babka wrote:
> On 4/13/22 18:39, David Hildenbrand wrote:
>>>> @@ -3035,10 +3083,19 @@ void set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw,
>>>>
>>>> flush_cache_range(vma, address, address + HPAGE_PMD_SIZE);
>>>> pmdval = pmdp_invalidate(vma, address, pvmw->pmd);
>>>> +
>>>> + anon_exclusive = PageAnon(page) && PageAnonExclusive(page);
>>>> + if (anon_exclusive && page_try_share_anon_rmap(page)) {
>>>> + set_pmd_at(mm, address, pvmw->pmd, pmdval);
>>>> + return;
>>>
>>> I am admittedly not too familiar with this code, but looks like this means
>>> we fail to migrate the THP, right? But we don't seem to be telling the
>>> caller, which is try_to_migrate_one(), so it will continue and not terminate
>>> the walk and return false?
>>
>> Right, we're not returning "false". Returning "false" would be an
>> optimization to make rmap_walk_anon() fail faster.
>
> Ah right, that's what I missed, it's an optimization and we will realize
> elsewhere afterwards that the page has still mappings and we can't migrate...
I'll include that patch in v4 (to be tested):
>From 08fb0e45404e3d0f85c2ad23a473e95053396376 Mon Sep 17 00:00:00 2001
From: David Hildenbrand <david@...hat.com>
Date: Tue, 19 Apr 2022 18:39:23 +0200
Subject: [PATCH] mm/rmap: fail try_to_migrate() early when setting a PMD
migration entry fails
Let's fail right away in case we cannot clear PG_anon_exclusive because
the anon THP may be pinned. Right now, we continue trying to
install migration entries and the caller of try_to_migrate() will
realize that the page is still mapped and has to restore the migration
entries. Let's just fail fast just like for PTE migration entries.
Suggested-by: Vlastimil Babka <vbabka@...e.cz>
Signed-off-by: David Hildenbrand <david@...hat.com>
---
include/linux/swapops.h | 4 ++--
mm/huge_memory.c | 8 +++++---
mm/rmap.c | 6 +++++-
3 files changed, 12 insertions(+), 6 deletions(-)
diff --git a/include/linux/swapops.h b/include/linux/swapops.h
index 06280fc1c99b..8b6e4cd1fab8 100644
--- a/include/linux/swapops.h
+++ b/include/linux/swapops.h
@@ -299,7 +299,7 @@ static inline bool is_pfn_swap_entry(swp_entry_t entry)
struct page_vma_mapped_walk;
#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
-extern void set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw,
+extern int set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw,
struct page *page);
extern void remove_migration_pmd(struct page_vma_mapped_walk *pvmw,
@@ -332,7 +332,7 @@ static inline int is_pmd_migration_entry(pmd_t pmd)
return !pmd_present(pmd) && is_migration_entry(pmd_to_swp_entry(pmd));
}
#else
-static inline void set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw,
+static inline int set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw,
struct page *page)
{
BUILD_BUG();
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index c7ac1b462543..390f22334ee9 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3080,7 +3080,7 @@ late_initcall(split_huge_pages_debugfs);
#endif
#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
-void set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw,
+int set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw,
struct page *page)
{
struct vm_area_struct *vma = pvmw->vma;
@@ -3092,7 +3092,7 @@ void set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw,
pmd_t pmdswp;
if (!(pvmw->pmd && !pvmw->pte))
- return;
+ return 0;
flush_cache_range(vma, address, address + HPAGE_PMD_SIZE);
pmdval = pmdp_invalidate(vma, address, pvmw->pmd);
@@ -3100,7 +3100,7 @@ void set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw,
anon_exclusive = PageAnon(page) && PageAnonExclusive(page);
if (anon_exclusive && page_try_share_anon_rmap(page)) {
set_pmd_at(mm, address, pvmw->pmd, pmdval);
- return;
+ return -EBUSY;
}
if (pmd_dirty(pmdval))
@@ -3118,6 +3118,8 @@ void set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw,
page_remove_rmap(page, vma, true);
put_page(page);
trace_set_migration_pmd(address, pmd_val(pmdswp));
+
+ return 0;
}
void remove_migration_pmd(struct page_vma_mapped_walk *pvmw, struct page *new)
diff --git a/mm/rmap.c b/mm/rmap.c
index 00418faaf4ce..68c2f61bf212 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1814,7 +1814,11 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
VM_BUG_ON_FOLIO(folio_test_hugetlb(folio) ||
!folio_test_pmd_mappable(folio), folio);
- set_pmd_migration_entry(&pvmw, subpage);
+ if (set_pmd_migration_entry(&pvmw, subpage)) {
+ ret = false;
+ page_vma_mapped_walk_done(&pvmw);
+ break;
+ }
continue;
}
#endif
--
2.35.1
--
Thanks,
David / dhildenb
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