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Message-ID: <ZtEHPAsIHKxUHBZX@bombadil.infradead.org>
Date: Thu, 29 Aug 2024 16:41:48 -0700
From: Luis Chamberlain <mcgrof@...nel.org>
To: Zi Yan <ziy@...dia.com>
Cc: Matthew Wilcox <willy@...radead.org>,
Sven Schnelle <svens@...ux.ibm.com>,
"Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>,
brauner@...nel.org, akpm@...ux-foundation.org,
chandan.babu@...cle.com, linux-fsdevel@...r.kernel.org,
djwong@...nel.org, hare@...e.de, gost.dev@...sung.com,
linux-xfs@...r.kernel.org, hch@....de, david@...morbit.com,
yang@...amperecomputing.com, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, john.g.garry@...cle.com,
cl@...amperecomputing.com, p.raghav@...sung.com,
ryan.roberts@....com, David Howells <dhowells@...hat.com>,
linux-s390@...r.kernel.org
Subject: Re: [PATCH v13 04/10] mm: split a folio in minimum folio order chunks
On Thu, Aug 29, 2024 at 06:12:26PM -0400, Zi Yan wrote:
> The issue is that the change to split_huge_page() makes split_huge_page_to_list_to_order()
> unlocks the wrong subpage. split_huge_page() used to pass the “page” pointer
> to split_huge_page_to_list_to_order(), which keeps that “page” still locked.
> But this patch changes the “page” passed into split_huge_page_to_list_to_order()
> always to the head page.
>
> This fixes the crash on my x86 VM, but it can be improved:
>
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index 7c50aeed0522..eff5d2fb5d4e 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -320,10 +320,7 @@ bool can_split_folio(struct folio *folio, int *pextra_pins);
> int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
> unsigned int new_order);
> int split_folio_to_list(struct folio *folio, struct list_head *list);
> -static inline int split_huge_page(struct page *page)
> -{
> - return split_folio(page_folio(page));
> -}
> +int split_huge_page(struct page *page);
> void deferred_split_folio(struct folio *folio);
>
> void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index c29af9451d92..4d723dab4336 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -3297,6 +3297,25 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
> return ret;
> }
>
> +int split_huge_page(struct page *page)
> +{
> + unsigned int min_order = 0;
> + struct folio *folio = page_folio(page);
> +
> + if (folio_test_anon(folio))
> + goto out;
> +
> + if (!folio->mapping) {
> + if (folio_test_pmd_mappable(folio))
> + count_vm_event(THP_SPLIT_PAGE_FAILED);
> + return -EBUSY;
> + }
> +
> + min_order = mapping_min_folio_order(folio->mapping);
> +out:
> + return split_huge_page_to_list_to_order(page, NULL, min_order);
> +}
> +
> int split_folio_to_list(struct folio *folio, struct list_head *list)
> {
> unsigned int min_order = 0;
Confirmed, and also although you suggest it can be improved, I thought
that we could do that by sharing more code and putting things in the
headers, the below also fixes this but tries to share more code, but
I think it is perhaps less easier to understand than your patch.
So I think your patch is cleaner and easier as a fix.
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index c275aa9cc105..99cd9c7bf55b 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -97,6 +97,7 @@ extern struct kobj_attribute thpsize_shmem_enabled_attr;
(!!thp_vma_allowable_orders(vma, vm_flags, tva_flags, BIT(order)))
#define split_folio(f) split_folio_to_list(f, NULL)
+#define split_folio_to_list(f, list) split_page_folio_to_list(&f->page, f, list)
#ifdef CONFIG_PGTABLE_HAS_HUGE_LEAVES
#define HPAGE_PMD_SHIFT PMD_SHIFT
@@ -331,10 +332,11 @@ unsigned long thp_get_unmapped_area_vmflags(struct file *filp, unsigned long add
bool can_split_folio(struct folio *folio, int caller_pins, int *pextra_pins);
int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
unsigned int new_order);
-int split_folio_to_list(struct folio *folio, struct list_head *list);
+int split_page_folio_to_list(struct page *page, struct folio *folio,
+ struct list_head *list);
static inline int split_huge_page(struct page *page)
{
- return split_folio(page_folio(page));
+ return split_page_folio_to_list(page, page_folio(page), NULL);
}
void deferred_split_folio(struct folio *folio);
@@ -511,7 +513,9 @@ static inline int split_huge_page(struct page *page)
return 0;
}
-static inline int split_folio_to_list(struct folio *folio, struct list_head *list)
+static inline int split_page_folio_to_list(struct page *page,
+ struct folio *folio,
+ struct list_head *list)
{
return 0;
}
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 169f1a71c95d..b115bfe63b52 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3529,7 +3529,8 @@ int split_huge_page_to_list_to_order(struct page *page, struct list_head *list,
return ret;
}
-int split_folio_to_list(struct folio *folio, struct list_head *list)
+int split_page_folio_to_list(struct page *page, struct folio *folio,
+ struct list_head *list)
{
unsigned int min_order = 0;
@@ -3544,8 +3545,7 @@ int split_folio_to_list(struct folio *folio, struct list_head *list)
min_order = mapping_min_folio_order(folio->mapping);
out:
- return split_huge_page_to_list_to_order(&folio->page, list,
- min_order);
+ return split_huge_page_to_list_to_order(page, list, min_order);
}
void __folio_undo_large_rmappable(struct folio *folio)
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