David Hildenbrand <david@xxxxxxxxxx> writes:
> On 09.03.20 03:17, Huang, Ying wrote:
>> From: Huang Ying <ying.huang@xxxxxxxxx>
>>
>> Now PageSwapBacked() is used as the helper function to check whether
>> pages have been freed lazily via MADV_FREE. This isn't very obvious.
>> So Dave suggested to add PageLazyFree() family helper functions to
>> improve the code readability.
>>
>> Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
>> Suggested-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
>> Cc: David Hildenbrand <david@xxxxxxxxxx>
>> Cc: Mel Gorman <mgorman@xxxxxxx>
>> Cc: Vlastimil Babka <vbabka@xxxxxxx>
>> Cc: Zi Yan <ziy@xxxxxxxxxx>
>> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
>> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
>> Cc: Minchan Kim <minchan@xxxxxxxxxx>
>> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
>> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
>> ---
>> Changelog:
>>
>> v3:
>>
>> - Improved comments, Thanks David Hildenbrand!
>>
>> - Use the helper function in /proc/PID/smaps lazyfree reporting.
>>
>> v2:
>>
>> - Avoid code bloat via removing VM_BUG_ON_PAGE(), which doesn't exist
>> in the original code. Now there is no any text/data/bss size
>> change.
>>
>> - Fix one wrong replacement in try_to_unmap_one().
>>
>> ---
>> fs/proc/task_mmu.c | 2 +-
>> include/linux/page-flags.h | 25 +++++++++++++++++++++++++
>> mm/rmap.c | 4 ++--
>> mm/swap.c | 11 +++--------
>> mm/vmscan.c | 7 +++----
>> 5 files changed, 34 insertions(+), 15 deletions(-)
>>
>> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
>> index 3ba9ae83bff5..3458d5711e57 100644
>> --- a/fs/proc/task_mmu.c
>> +++ b/fs/proc/task_mmu.c
>> @@ -471,7 +471,7 @@ static void smaps_account(struct mem_size_stats *mss, struct page *page,
>> */
>> if (PageAnon(page)) {
>> mss->anonymous += size;
>> - if (!PageSwapBacked(page) && !dirty && !PageDirty(page))
>> + if (__PageLazyFree(page) && !dirty && !PageDirty(page))
>> mss->lazyfree += size;
>> }
>>
>> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
>> index 49c2697046b9..bb26f74cbe8e 100644
>> --- a/include/linux/page-flags.h
>> +++ b/include/linux/page-flags.h
>> @@ -498,6 +498,31 @@ static __always_inline int PageKsm(struct page *page)
>> TESTPAGEFLAG_FALSE(Ksm)
>> #endif
>>
>> +/*
>> + * For pages freed lazily via MADV_FREE. Lazyfree pages are clean
>> + * anonymous pages. They don't have PG_swapbacked set, to distinguish
>> + * them from normal anonymous pages.
>> + */
>> +static __always_inline int __PageLazyFree(struct page *page)
>> +{
>> + return !PageSwapBacked(page);
>> +}
>> +
>> +static __always_inline int PageLazyFree(struct page *page)
>> +{
>> + return PageAnon(page) && __PageLazyFree(page);
>> +}
>> +
>> +static __always_inline void SetPageLazyFree(struct page *page)
>> +{
>> + ClearPageSwapBacked(page);
>> +}
>> +
>> +static __always_inline void ClearPageLazyFree(struct page *page)
>> +{
>> + SetPageSwapBacked(page);
>> +}
>> +
>> u64 stable_page_flags(struct page *page);
>>
>> static inline int PageUptodate(struct page *page)
>> diff --git a/mm/rmap.c b/mm/rmap.c
>> index 1c02adaa233e..6ec96c8e7826 100644
>> --- a/mm/rmap.c
>> +++ b/mm/rmap.c
>> @@ -1609,7 +1609,7 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
>> }
>>
>> /* MADV_FREE page check */
>> - if (!PageSwapBacked(page)) {
>> + if (__PageLazyFree(page)) {
>> if (!PageDirty(page)) {
>> /* Invalidate as we cleared the pte */
>> mmu_notifier_invalidate_range(mm,
>> @@ -1623,7 +1623,7 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
>> * discarded. Remap the page to page table.
>> */
>> set_pte_at(mm, address, pvmw.pte, pteval);
>> - SetPageSwapBacked(page);
>> + ClearPageLazyFree(page);
>> ret = false;
>> page_vma_mapped_walk_done(&pvmw);
>> break;
>> diff --git a/mm/swap.c b/mm/swap.c
>> index c1d3ca80ea10..d83f2cd4cdb8 100644
>> --- a/mm/swap.c
>> +++ b/mm/swap.c
>> @@ -563,7 +563,7 @@ static void lru_deactivate_fn(struct page *page, struct lruvec *lruvec,
>> static void lru_lazyfree_fn(struct page *page, struct lruvec *lruvec,
>> void *arg)
>> {
>> - if (PageLRU(page) && PageAnon(page) && PageSwapBacked(page) &&
>> + if (PageLRU(page) && PageAnon(page) && !__PageLazyFree(page) &&
>> !PageSwapCache(page) && !PageUnevictable(page)) {
>> bool active = PageActive(page);
>>
>> @@ -571,12 +571,7 @@ static void lru_lazyfree_fn(struct page *page, struct lruvec *lruvec,
>> LRU_INACTIVE_ANON + active);
>> ClearPageActive(page);
>> ClearPageReferenced(page);
>> - /*
>> - * lazyfree pages are clean anonymous pages. They have
>> - * SwapBacked flag cleared to distinguish normal anonymous
>> - * pages
>> - */
>> - ClearPageSwapBacked(page);
>> + SetPageLazyFree(page);
>> add_page_to_lru_list(page, lruvec, LRU_INACTIVE_FILE);
>>
>> __count_vm_events(PGLAZYFREE, hpage_nr_pages(page));
>> @@ -678,7 +673,7 @@ void deactivate_page(struct page *page)
>> */
>> void mark_page_lazyfree(struct page *page)
>> {
>> - if (PageLRU(page) && PageAnon(page) && PageSwapBacked(page) &&
>> + if (PageLRU(page) && PageAnon(page) && !__PageLazyFree(page) &&
>> !PageSwapCache(page) && !PageUnevictable(page)) {
>> struct pagevec *pvec = &get_cpu_var(lru_lazyfree_pvecs);
>>
>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>> index eca49a1c2f68..40bb41ada2d2 100644
>> --- a/mm/vmscan.c
>> +++ b/mm/vmscan.c
>> @@ -1043,8 +1043,7 @@ static void page_check_dirty_writeback(struct page *page,
>> * Anonymous pages are not handled by flushers and must be written
>> * from reclaim context. Do not stall reclaim based on them
>> */
>> - if (!page_is_file_cache(page) ||
>> - (PageAnon(page) && !PageSwapBacked(page))) {
>> + if (!page_is_file_cache(page) || PageLazyFree(page)) {
>> *dirty = false;
>> *writeback = false;
>> return;
>> @@ -1235,7 +1234,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
>> * Try to allocate it some swap space here.
>> * Lazyfree page could be freed directly
>> */
>> - if (PageAnon(page) && PageSwapBacked(page)) {
>> + if (PageAnon(page) && !__PageLazyFree(page)) {
>> if (!PageSwapCache(page)) {
>> if (!(sc->gfp_mask & __GFP_IO))
>> goto keep_locked;
>> @@ -1411,7 +1410,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
>> }
>> }
>>
>> - if (PageAnon(page) && !PageSwapBacked(page)) {
>> + if (PageLazyFree(page)) {
>> /* follow __remove_mapping for reference */
>> if (!page_ref_freeze(page, 1))
>> goto keep_locked;
>>
>
> I still prefer something like
>
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index fd6d4670ccc3..7538501230bd 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -63,6 +63,10 @@
> * page_waitqueue(page) is a wait queue of all tasks waiting for the page
> * to become unlocked.
> *
> + * PG_swapbacked used with anonymous pages (PageAnon()) indicates that a
> + * page is backed by swap. Anonymous pages without PG_swapbacked are
> + * pages that can be lazily freed (e.g., MADV_FREE) on demand.
> + *
> * PG_uptodate tells whether the page's contents is valid. When a read
> * completes, the page becomes uptodate, unless a disk I/O error happened.
> *
Why not just send a formal patch? So Andrew can just pick anything he
likes. I am totally OK with that.
> and really don't like the use of !__PageLazyFree() instead of PageSwapBacked().
If adopted, !__PageLazyFree() should only be used in the context where
we really want to check whether pages are freed lazily. Otherwise,
PageSwapBacked() should be used.
Best Regards,
Huang, Ying
