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Message-ID: <20230821160849.531668-2-david@redhat.com>
Date: Mon, 21 Aug 2023 18:08:46 +0200
From: David Hildenbrand <david@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org, linux-arm-kernel@...ts.infradead.org,
David Hildenbrand <david@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Matthew Wilcox <willy@...radead.org>,
Peter Xu <peterx@...hat.com>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>, Hugh Dickins <hughd@...gle.com>,
Seth Jennings <sjenning@...hat.com>,
Dan Streetman <ddstreet@...e.org>,
Vitaly Wool <vitaly.wool@...sulko.com>
Subject: [PATCH mm-unstable v1 1/4] mm/swap: stop using page->private on tail pages for THP_SWAP
Let's stop using page->private on tail pages, making it possible to
just unconditionally reuse that field in the tail pages of large folios.
The remaining usage of the private field for THP_SWAP is in the THP
splitting code (mm/huge_memory.c), that we'll handle separately later.
Update the THP_SWAP documentation and sanity checks in mm_types.h and
__split_huge_page_tail().
Signed-off-by: David Hildenbrand <david@...hat.com>
---
arch/arm64/mm/mteswap.c | 5 +++--
include/linux/mm_types.h | 12 +-----------
include/linux/swap.h | 9 +++++++++
mm/huge_memory.c | 15 ++++++---------
mm/memory.c | 2 +-
mm/rmap.c | 2 +-
mm/swap_state.c | 5 +++--
mm/swapfile.c | 4 ++--
8 files changed, 26 insertions(+), 28 deletions(-)
diff --git a/arch/arm64/mm/mteswap.c b/arch/arm64/mm/mteswap.c
index cd508ba80ab1..a31833e3ddc5 100644
--- a/arch/arm64/mm/mteswap.c
+++ b/arch/arm64/mm/mteswap.c
@@ -33,8 +33,9 @@ int mte_save_tags(struct page *page)
mte_save_page_tags(page_address(page), tag_storage);
- /* page_private contains the swap entry.val set in do_swap_page */
- ret = xa_store(&mte_pages, page_private(page), tag_storage, GFP_KERNEL);
+ /* lookup the swap entry.val from the page */
+ ret = xa_store(&mte_pages, page_swap_entry(page).val, tag_storage,
+ GFP_KERNEL);
if (WARN(xa_is_err(ret), "Failed to store MTE tags")) {
mte_free_tag_storage(tag_storage);
return xa_err(ret);
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index b9b6c88875b9..61361f1750c3 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -333,11 +333,8 @@ struct folio {
atomic_t _pincount;
#ifdef CONFIG_64BIT
unsigned int _folio_nr_pages;
- /* 4 byte gap here */
- /* private: the union with struct page is transitional */
- /* Fix THP_SWAP to not use tail->private */
- unsigned long _private_1;
#endif
+ /* private: the union with struct page is transitional */
};
struct page __page_1;
};
@@ -358,9 +355,6 @@ struct folio {
/* public: */
struct list_head _deferred_list;
/* private: the union with struct page is transitional */
- unsigned long _avail_2a;
- /* Fix THP_SWAP to not use tail->private */
- unsigned long _private_2a;
};
struct page __page_2;
};
@@ -385,9 +379,6 @@ FOLIO_MATCH(memcg_data, memcg_data);
offsetof(struct page, pg) + sizeof(struct page))
FOLIO_MATCH(flags, _flags_1);
FOLIO_MATCH(compound_head, _head_1);
-#ifdef CONFIG_64BIT
-FOLIO_MATCH(private, _private_1);
-#endif
#undef FOLIO_MATCH
#define FOLIO_MATCH(pg, fl) \
static_assert(offsetof(struct folio, fl) == \
@@ -396,7 +387,6 @@ FOLIO_MATCH(flags, _flags_2);
FOLIO_MATCH(compound_head, _head_2);
FOLIO_MATCH(flags, _flags_2a);
FOLIO_MATCH(compound_head, _head_2a);
-FOLIO_MATCH(private, _private_2a);
#undef FOLIO_MATCH
/**
diff --git a/include/linux/swap.h b/include/linux/swap.h
index bb5adc604144..84fe0e94f5cd 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -339,6 +339,15 @@ static inline swp_entry_t folio_swap_entry(struct folio *folio)
return entry;
}
+static inline swp_entry_t page_swap_entry(struct page *page)
+{
+ struct folio *folio = page_folio(page);
+ swp_entry_t entry = folio_swap_entry(folio);
+
+ entry.val += page - &folio->page;
+ return entry;
+}
+
static inline void folio_set_swap_entry(struct folio *folio, swp_entry_t entry)
{
folio->private = (void *)entry.val;
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index cc2f65f8cc62..c04702ae71d2 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2446,18 +2446,15 @@ static void __split_huge_page_tail(struct page *head, int tail,
page_tail->index = head->index + tail;
/*
- * page->private should not be set in tail pages with the exception
- * of swap cache pages that store the swp_entry_t in tail pages.
- * Fix up and warn once if private is unexpectedly set.
- *
- * What of 32-bit systems, on which folio->_pincount overlays
- * head[1].private? No problem: THP_SWAP is not enabled on 32-bit, and
- * pincount must be 0 for folio_ref_freeze() to have succeeded.
+ * page->private should not be set in tail pages. Fix up and warn once
+ * if private is unexpectedly set.
*/
- if (!folio_test_swapcache(page_folio(head))) {
- VM_WARN_ON_ONCE_PAGE(page_tail->private != 0, page_tail);
+ if (unlikely(page_tail->private)) {
+ VM_WARN_ON_ONCE_PAGE(true, page_tail);
page_tail->private = 0;
}
+ if (PageSwapCache(head))
+ set_page_private(page_tail, (unsigned long)head->private + tail);
/* Page flags must be visible before we make the page non-compound. */
smp_wmb();
diff --git a/mm/memory.c b/mm/memory.c
index d003076b218d..ff13242c1589 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3882,7 +3882,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
* changed.
*/
if (unlikely(!folio_test_swapcache(folio) ||
- page_private(page) != entry.val))
+ page_swap_entry(page).val != entry.val))
goto out_page;
/*
diff --git a/mm/rmap.c b/mm/rmap.c
index 1f04debdc87a..ec7f8e6c9e48 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1647,7 +1647,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
*/
dec_mm_counter(mm, mm_counter(&folio->page));
} else if (folio_test_anon(folio)) {
- swp_entry_t entry = { .val = page_private(subpage) };
+ swp_entry_t entry = page_swap_entry(subpage);
pte_t swp_pte;
/*
* Store the swap location in the pte.
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 01f15139b7d9..2f2417810052 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -100,6 +100,7 @@ int add_to_swap_cache(struct folio *folio, swp_entry_t entry,
folio_ref_add(folio, nr);
folio_set_swapcache(folio);
+ folio_set_swap_entry(folio, entry);
do {
xas_lock_irq(&xas);
@@ -113,7 +114,6 @@ int add_to_swap_cache(struct folio *folio, swp_entry_t entry,
if (shadowp)
*shadowp = old;
}
- set_page_private(folio_page(folio, i), entry.val + i);
xas_store(&xas, folio);
xas_next(&xas);
}
@@ -154,9 +154,10 @@ void __delete_from_swap_cache(struct folio *folio,
for (i = 0; i < nr; i++) {
void *entry = xas_store(&xas, shadow);
VM_BUG_ON_PAGE(entry != folio, entry);
- set_page_private(folio_page(folio, i), 0);
xas_next(&xas);
}
+ entry.val = 0;
+ folio_set_swap_entry(folio, entry);
folio_clear_swapcache(folio);
address_space->nrpages -= nr;
__node_stat_mod_folio(folio, NR_FILE_PAGES, -nr);
diff --git a/mm/swapfile.c b/mm/swapfile.c
index d46933adf789..bd9d904671b9 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -3369,7 +3369,7 @@ struct swap_info_struct *swp_swap_info(swp_entry_t entry)
struct swap_info_struct *page_swap_info(struct page *page)
{
- swp_entry_t entry = { .val = page_private(page) };
+ swp_entry_t entry = page_swap_entry(page);
return swp_swap_info(entry);
}
@@ -3384,7 +3384,7 @@ EXPORT_SYMBOL_GPL(swapcache_mapping);
pgoff_t __page_file_index(struct page *page)
{
- swp_entry_t swap = { .val = page_private(page) };
+ swp_entry_t swap = page_swap_entry(page);
return swp_offset(swap);
}
EXPORT_SYMBOL_GPL(__page_file_index);
--
2.41.0
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