[PATCH RFC v2 5/5] mm: support large folios swapin as a whole
Barry Song
21cnbao at gmail.com
Wed Feb 28 16:37:53 PST 2024
From: Chuanhua Han <hanchuanhua at oppo.com>
On an embedded system like Android, more than half of anon memory is actually
in swap devices such as zRAM. For example, while an app is switched to back-
ground, its most memory might be swapped-out.
Now we have mTHP features, unfortunately, if we don't support large folios
swap-in, once those large folios are swapped-out, we immediately lose the
performance gain we can get through large folios and hardware optimization
such as CONT-PTE.
This patch brings up mTHP swap-in support. Right now, we limit mTHP swap-in
to those contiguous swaps which were likely swapped out from mTHP as a whole.
On the other hand, the current implementation only covers the SWAP_SYCHRONOUS
case. It doesn't support swapin_readahead as large folios yet.
Right now, we are re-faulting large folios which are still in swapcache as a
whole, this can effectively decrease extra loops and early-exitings which we
have increased in arch_swap_restore() while supporting MTE restore for folios
rather than page. On the other hand, it can also decrease do_swap_page as PTEs
used to be set one by one even we hit a large folio in swapcache.
Signed-off-by: Chuanhua Han <hanchuanhua at oppo.com>
Co-developed-by: Barry Song <v-songbaohua at oppo.com>
Signed-off-by: Barry Song <v-songbaohua at oppo.com>
---
mm/memory.c | 191 ++++++++++++++++++++++++++++++++++++++++++----------
1 file changed, 157 insertions(+), 34 deletions(-)
diff --git a/mm/memory.c b/mm/memory.c
index 90b08b7cbaac..471689ce4e91 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -104,9 +104,16 @@ struct page *mem_map;
EXPORT_SYMBOL(mem_map);
#endif
+/* A choice of behaviors for alloc_anon_folio() */
+enum behavior {
+ DO_SWAP_PAGE,
+ DO_ANON_PAGE,
+};
+
static vm_fault_t do_fault(struct vm_fault *vmf);
static vm_fault_t do_anonymous_page(struct vm_fault *vmf);
static bool vmf_pte_changed(struct vm_fault *vmf);
+static struct folio *alloc_anon_folio(struct vm_fault *vmf, enum behavior behavior);
/*
* Return true if the original pte was a uffd-wp pte marker (so the pte was
@@ -3974,6 +3981,52 @@ static vm_fault_t handle_pte_marker(struct vm_fault *vmf)
return VM_FAULT_SIGBUS;
}
+/*
+ * check a range of PTEs are completely swap entries with
+ * contiguous swap offsets and the same SWAP_HAS_CACHE.
+ * pte must be first one in the range
+ */
+static bool is_pte_range_contig_swap(pte_t *pte, int nr_pages)
+{
+ int i;
+ struct swap_info_struct *si;
+ swp_entry_t entry;
+ unsigned type;
+ pgoff_t start_offset;
+ char has_cache;
+
+ entry = pte_to_swp_entry(ptep_get_lockless(pte));
+ if (non_swap_entry(entry))
+ return false;
+ start_offset = swp_offset(entry);
+ if (start_offset % nr_pages)
+ return false;
+
+ si = swp_swap_info(entry);
+ type = swp_type(entry);
+ has_cache = si->swap_map[start_offset] & SWAP_HAS_CACHE;
+ for (i = 1; i < nr_pages; i++) {
+ entry = pte_to_swp_entry(ptep_get_lockless(pte + i));
+ if (non_swap_entry(entry))
+ return false;
+ if (swp_offset(entry) != start_offset + i)
+ return false;
+ if (swp_type(entry) != type)
+ return false;
+ /*
+ * while allocating a large folio and doing swap_read_folio for the
+ * SWP_SYNCHRONOUS_IO path, which is the case the being faulted pte
+ * doesn't have swapcache. We need to ensure all PTEs have no cache
+ * as well, otherwise, we might go to swap devices while the content
+ * is in swapcache
+ */
+ if ((si->swap_map[start_offset + i] & SWAP_HAS_CACHE) != has_cache)
+ return false;
+ }
+
+ return true;
+}
+
/*
* We enter with non-exclusive mmap_lock (to exclude vma changes,
* but allow concurrent faults), and pte mapped but not yet locked.
@@ -3995,6 +4048,9 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
pte_t pte;
vm_fault_t ret = 0;
void *shadow = NULL;
+ int nr_pages = 1;
+ unsigned long start_address;
+ pte_t *start_pte;
if (!pte_unmap_same(vmf))
goto out;
@@ -4058,28 +4114,32 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
if (!folio) {
if (data_race(si->flags & SWP_SYNCHRONOUS_IO) &&
__swap_count(entry) == 1) {
- /*
- * Prevent parallel swapin from proceeding with
- * the cache flag. Otherwise, another thread may
- * finish swapin first, free the entry, and swapout
- * reusing the same entry. It's undetectable as
- * pte_same() returns true due to entry reuse.
- */
- if (swapcache_prepare(entry)) {
- /* Relax a bit to prevent rapid repeated page faults */
- schedule_timeout_uninterruptible(1);
- goto out;
- }
- need_clear_cache = true;
-
/* skip swapcache */
- folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0,
- vma, vmf->address, false);
+ folio = alloc_anon_folio(vmf, DO_SWAP_PAGE);
page = &folio->page;
if (folio) {
__folio_set_locked(folio);
__folio_set_swapbacked(folio);
+ if (folio_test_large(folio)) {
+ nr_pages = folio_nr_pages(folio);
+ entry.val = ALIGN_DOWN(entry.val, nr_pages);
+ }
+
+ /*
+ * Prevent parallel swapin from proceeding with
+ * the cache flag. Otherwise, another thread may
+ * finish swapin first, free the entry, and swapout
+ * reusing the same entry. It's undetectable as
+ * pte_same() returns true due to entry reuse.
+ */
+ if (swapcache_prepare_nr(entry, nr_pages)) {
+ /* Relax a bit to prevent rapid repeated page faults */
+ schedule_timeout_uninterruptible(1);
+ goto out;
+ }
+ need_clear_cache = true;
+
if (mem_cgroup_swapin_charge_folio(folio,
vma->vm_mm, GFP_KERNEL,
entry)) {
@@ -4185,6 +4245,42 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
*/
vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, vmf->address,
&vmf->ptl);
+
+ start_address = vmf->address;
+ start_pte = vmf->pte;
+ if (folio_test_large(folio)) {
+ unsigned long nr = folio_nr_pages(folio);
+ unsigned long addr = ALIGN_DOWN(vmf->address, nr * PAGE_SIZE);
+ pte_t *aligned_pte = vmf->pte - (vmf->address - addr) / PAGE_SIZE;
+
+ /*
+ * case 1: we are allocating large_folio, try to map it as a whole
+ * iff the swap entries are still entirely mapped;
+ * case 2: we hit a large folio in swapcache, and all swap entries
+ * are still entirely mapped, try to map a large folio as a whole.
+ * otherwise, map only the faulting page within the large folio
+ * which is swapcache
+ */
+ if (!is_pte_range_contig_swap(aligned_pte, nr)) {
+ if (nr_pages > 1) /* ptes have changed for case 1 */
+ goto out_nomap;
+ goto check_pte;
+ }
+
+ start_address = addr;
+ start_pte = aligned_pte;
+ /*
+ * the below has been done before swap_read_folio()
+ * for case 1
+ */
+ if (unlikely(folio == swapcache)) {
+ nr_pages = nr;
+ entry.val = ALIGN_DOWN(entry.val, nr_pages);
+ page = &folio->page;
+ }
+ }
+
+check_pte:
if (unlikely(!vmf->pte || !pte_same(ptep_get(vmf->pte), vmf->orig_pte)))
goto out_nomap;
@@ -4252,12 +4348,14 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
* We're already holding a reference on the page but haven't mapped it
* yet.
*/
- swap_free(entry);
+ swap_nr_free(entry, nr_pages);
if (should_try_to_free_swap(folio, vma, vmf->flags))
folio_free_swap(folio);
- inc_mm_counter(vma->vm_mm, MM_ANONPAGES);
- dec_mm_counter(vma->vm_mm, MM_SWAPENTS);
+ folio_ref_add(folio, nr_pages - 1);
+ add_mm_counter(vma->vm_mm, MM_ANONPAGES, nr_pages);
+ add_mm_counter(vma->vm_mm, MM_SWAPENTS, -nr_pages);
+
pte = mk_pte(page, vma->vm_page_prot);
/*
@@ -4267,14 +4365,14 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
* exclusivity.
*/
if (!folio_test_ksm(folio) &&
- (exclusive || folio_ref_count(folio) == 1)) {
+ (exclusive || folio_ref_count(folio) == nr_pages)) {
if (vmf->flags & FAULT_FLAG_WRITE) {
pte = maybe_mkwrite(pte_mkdirty(pte), vma);
vmf->flags &= ~FAULT_FLAG_WRITE;
}
rmap_flags |= RMAP_EXCLUSIVE;
}
- flush_icache_page(vma, page);
+ flush_icache_pages(vma, page, nr_pages);
if (pte_swp_soft_dirty(vmf->orig_pte))
pte = pte_mksoft_dirty(pte);
if (pte_swp_uffd_wp(vmf->orig_pte))
@@ -4283,17 +4381,19 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
/* ksm created a completely new copy */
if (unlikely(folio != swapcache && swapcache)) {
- folio_add_new_anon_rmap(folio, vma, vmf->address);
+ folio_add_new_anon_rmap(folio, vma, start_address);
folio_add_lru_vma(folio, vma);
+ } else if (!folio_test_anon(folio)) {
+ folio_add_new_anon_rmap(folio, vma, start_address);
} else {
- folio_add_anon_rmap_pte(folio, page, vma, vmf->address,
+ folio_add_anon_rmap_ptes(folio, page, nr_pages, vma, start_address,
rmap_flags);
}
VM_BUG_ON(!folio_test_anon(folio) ||
(pte_write(pte) && !PageAnonExclusive(page)));
- set_pte_at(vma->vm_mm, vmf->address, vmf->pte, pte);
- arch_do_swap_page(vma->vm_mm, vma, vmf->address, pte, vmf->orig_pte);
+ set_ptes(vma->vm_mm, start_address, start_pte, pte, nr_pages);
+ arch_do_swap_page(vma->vm_mm, vma, start_address, pte, vmf->orig_pte);
folio_unlock(folio);
if (folio != swapcache && swapcache) {
@@ -4310,6 +4410,9 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
}
if (vmf->flags & FAULT_FLAG_WRITE) {
+ if (nr_pages > 1)
+ vmf->orig_pte = ptep_get(vmf->pte);
+
ret |= do_wp_page(vmf);
if (ret & VM_FAULT_ERROR)
ret &= VM_FAULT_ERROR;
@@ -4317,14 +4420,14 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
}
/* No need to invalidate - it was non-present before */
- update_mmu_cache_range(vmf, vma, vmf->address, vmf->pte, 1);
+ update_mmu_cache_range(vmf, vma, start_address, start_pte, nr_pages);
unlock:
if (vmf->pte)
pte_unmap_unlock(vmf->pte, vmf->ptl);
out:
/* Clear the swap cache pin for direct swapin after PTL unlock */
if (need_clear_cache)
- swapcache_clear(si, entry);
+ swapcache_clear_nr(si, entry, nr_pages);
if (si)
put_swap_device(si);
return ret;
@@ -4340,7 +4443,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
folio_put(swapcache);
}
if (need_clear_cache)
- swapcache_clear(si, entry);
+ swapcache_clear_nr(si, entry, nr_pages);
if (si)
put_swap_device(si);
return ret;
@@ -4358,7 +4461,7 @@ static bool pte_range_none(pte_t *pte, int nr_pages)
return true;
}
-static struct folio *alloc_anon_folio(struct vm_fault *vmf)
+static struct folio *alloc_anon_folio(struct vm_fault *vmf, enum behavior behavior)
{
struct vm_area_struct *vma = vmf->vma;
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
@@ -4376,6 +4479,19 @@ static struct folio *alloc_anon_folio(struct vm_fault *vmf)
if (unlikely(userfaultfd_armed(vma)))
goto fallback;
+ /*
+ * a large folio being swapped-in could be partially in
+ * zswap and partially in swap devices, zswap doesn't
+ * support large folios yet, we might get corrupted
+ * zero-filled data by reading all subpages from swap
+ * devices while some of them are actually in zswap
+ */
+ if (behavior == DO_SWAP_PAGE && is_zswap_enabled())
+ goto fallback;
+
+ if (unlikely(behavior != DO_ANON_PAGE && behavior != DO_SWAP_PAGE))
+ return ERR_PTR(-EINVAL);
+
/*
* Get a list of all the (large) orders below PMD_ORDER that are enabled
* for this vma. Then filter out the orders that can't be allocated over
@@ -4393,15 +4509,22 @@ static struct folio *alloc_anon_folio(struct vm_fault *vmf)
return ERR_PTR(-EAGAIN);
/*
- * Find the highest order where the aligned range is completely
- * pte_none(). Note that all remaining orders will be completely
+ * For do_anonymous_page, find the highest order where the aligned range is
+ * completely pte_none(). Note that all remaining orders will be completely
* pte_none().
+ * For do_swap_page, find the highest order where the aligned range is
+ * completely swap entries with contiguous swap offsets.
*/
order = highest_order(orders);
while (orders) {
addr = ALIGN_DOWN(vmf->address, PAGE_SIZE << order);
- if (pte_range_none(pte + pte_index(addr), 1 << order))
- break;
+ if (behavior == DO_ANON_PAGE) {
+ if (pte_range_none(pte + pte_index(addr), 1 << order))
+ break;
+ } else {
+ if (is_pte_range_contig_swap(pte + pte_index(addr), 1 << order))
+ break;
+ }
order = next_order(&orders, order);
}
@@ -4485,7 +4608,7 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
if (unlikely(anon_vma_prepare(vma)))
goto oom;
/* Returns NULL on OOM or ERR_PTR(-EAGAIN) if we must retry the fault */
- folio = alloc_anon_folio(vmf);
+ folio = alloc_anon_folio(vmf, DO_ANON_PAGE);
if (IS_ERR(folio))
return 0;
if (!folio)
--
2.34.1
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