On 25/08/2023 14:59, Matthew Wilcox (Oracle) wrote:
> By making release_pages() call folios_put(), we can get rid of the calls
> to compound_head() for the callers that already know they have folios.
> We can also get rid of the lock_batch tracking as we know the size of
> the batch is limited by folio_batch.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> ---
> include/linux/mm.h | 19 ++---------
> mm/mlock.c | 3 +-
> mm/swap.c | 84 +++++++++++++++++++++++++++-------------------
> 3 files changed, 52 insertions(+), 54 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 2c6b54b5506a..7d1d96b75d11 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -36,6 +36,7 @@ struct anon_vma;
> struct anon_vma_chain;
> struct user_struct;
> struct pt_regs;
> +struct folio_batch;
>
> extern int sysctl_page_lock_unfairness;
>
> @@ -1521,23 +1522,7 @@ typedef union {
> } release_pages_arg __attribute__ ((__transparent_union__));
>
> void release_pages(release_pages_arg, int nr);
> -
> -/**
> - * folios_put - Decrement the reference count on an array of folios.
> - * @folios: The folios.
> - * @nr: How many folios there are.
> - *
> - * Like folio_put(), but for an array of folios. This is more efficient
> - * than writing the loop yourself as it will optimise the locks which
> - * need to be taken if the folios are freed.
> - *
> - * Context: May be called in process or interrupt context, but not in NMI
> - * context. May be called while holding a spinlock.
> - */
> -static inline void folios_put(struct folio **folios, unsigned int nr)
> -{
> - release_pages(folios, nr);
> -}
> +void folios_put(struct folio_batch *folios);
>
> static inline void put_page(struct page *page)
> {
> diff --git a/mm/mlock.c b/mm/mlock.c
> index 06bdfab83b58..67bd74a6268a 100644
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -206,8 +206,7 @@ static void mlock_folio_batch(struct folio_batch *fbatch)
>
> if (lruvec)
> unlock_page_lruvec_irq(lruvec);
> - folios_put(fbatch->folios, folio_batch_count(fbatch));
> - folio_batch_reinit(fbatch);
> + folios_put(fbatch);
> }
>
> void mlock_drain_local(void)
> diff --git a/mm/swap.c b/mm/swap.c
> index cd8f0150ba3a..7bdc63b56859 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -89,7 +89,7 @@ static void __page_cache_release(struct folio *folio)
> __folio_clear_lru_flags(folio);
> unlock_page_lruvec_irqrestore(lruvec, flags);
> }
> - /* See comment on folio_test_mlocked in release_pages() */
> + /* See comment on folio_test_mlocked in folios_put() */
> if (unlikely(folio_test_mlocked(folio))) {
> long nr_pages = folio_nr_pages(folio);
>
> @@ -175,7 +175,7 @@ static void lru_add_fn(struct lruvec *lruvec, struct folio *folio)
> * while the LRU lock is held.
> *
> * (That is not true of __page_cache_release(), and not necessarily
> - * true of release_pages(): but those only clear the mlocked flag after
> + * true of folios_put(): but those only clear the mlocked flag after
> * folio_put_testzero() has excluded any other users of the folio.)
> */
> if (folio_evictable(folio)) {
> @@ -221,8 +221,7 @@ static void folio_batch_move_lru(struct folio_batch *fbatch, move_fn_t move_fn)
>
> if (lruvec)
> unlock_page_lruvec_irqrestore(lruvec, flags);
> - folios_put(fbatch->folios, folio_batch_count(fbatch));
> - folio_batch_reinit(fbatch);
> + folios_put(fbatch);
> }
>
> static void folio_batch_add_and_move(struct folio_batch *fbatch,
> @@ -946,41 +945,27 @@ void lru_cache_disable(void)
> }
>
> /**
> - * release_pages - batched put_page()
> - * @arg: array of pages to release
> - * @nr: number of pages
> + * folios_put - Decrement the reference count on a batch of folios.
> + * @folios: The folios.
> *
> - * Decrement the reference count on all the pages in @arg. If it
> - * fell to zero, remove the page from the LRU and free it.
> + * Like folio_put(), but for a batch of folios. This is more efficient
> + * than writing the loop yourself as it will optimise the locks which need
> + * to be taken if the folios are freed. The folios batch is returned
> + * empty and ready to be reused for another batch; there is no need to
> + * reinitialise it.
> *
> - * Note that the argument can be an array of pages, encoded pages,
> - * or folio pointers. We ignore any encoded bits, and turn any of
> - * them into just a folio that gets free'd.
> + * Context: May be called in process or interrupt context, but not in NMI
> + * context. May be called while holding a spinlock.
> */
> -void release_pages(release_pages_arg arg, int nr)
> +void folios_put(struct folio_batch *folios)
> {
> int i;
> - struct encoded_page **encoded = arg.encoded_pages;
> LIST_HEAD(pages_to_free);
> struct lruvec *lruvec = NULL;
> unsigned long flags = 0;
> - unsigned int lock_batch;
>
> - for (i = 0; i < nr; i++) {
> - struct folio *folio;
> -
> - /* Turn any of the argument types into a folio */
> - folio = page_folio(encoded_page_ptr(encoded[i]));
> -
> - /*
> - * Make sure the IRQ-safe lock-holding time does not get
> - * excessive with a continuous string of pages from the
> - * same lruvec. The lock is held only if lruvec != NULL.
> - */
> - if (lruvec && ++lock_batch == SWAP_CLUSTER_MAX) {
SWAP_CLUSTER_MAX is 32. By using the folio_batch, I think you are limitted to 15
in your batch, so I guess you could be taking/releasing the lock x2 as often? Is
there any perf implication?
> - unlock_page_lruvec_irqrestore(lruvec, flags);
> - lruvec = NULL;
> - }
> + for (i = 0; i < folios->nr; i++) {
> + struct folio *folio = folios->folios[i];
>
> if (is_huge_zero_page(&folio->page))
> continue;
> @@ -1010,13 +995,8 @@ void release_pages(release_pages_arg arg, int nr)
> }
>
> if (folio_test_lru(folio)) {
> - struct lruvec *prev_lruvec = lruvec;
> -
> lruvec = folio_lruvec_relock_irqsave(folio, lruvec,
> &flags);
> - if (prev_lruvec != lruvec)
> - lock_batch = 0;
> -
> lruvec_del_folio(lruvec, folio);
> __folio_clear_lru_flags(folio);
> }
> @@ -1040,6 +1020,40 @@ void release_pages(release_pages_arg arg, int nr)
>
> mem_cgroup_uncharge_list(&pages_to_free);
> free_unref_page_list(&pages_to_free);
> + folios->nr = 0;
folio_batch_reinit(folios) ?
> +}
> +EXPORT_SYMBOL(folios_put);
> +
> +/**
> + * release_pages - batched put_page()
> + * @arg: array of pages to release
> + * @nr: number of pages
> + *
> + * Decrement the reference count on all the pages in @arg. If it
> + * fell to zero, remove the page from the LRU and free it.
> + *
> + * Note that the argument can be an array of pages, encoded pages,
> + * or folio pointers. We ignore any encoded bits, and turn any of
> + * them into just a folio that gets free'd.
> + */
> +void release_pages(release_pages_arg arg, int nr)
> +{
> + struct folio_batch fbatch;
> + struct encoded_page **encoded = arg.encoded_pages;
> + int i;
> +
> + folio_batch_init(&fbatch);
> + for (i = 0; i < nr; i++) {
> + /* Turn any of the argument types into a folio */
> + struct folio *folio = page_folio(encoded_page_ptr(encoded[i]));
> +
> + if (folio_batch_add(&fbatch, folio) > 0)
> + continue;
> + folios_put(&fbatch);
> + }
> +
> + if (fbatch.nr)
if (folio_batch_count(&fbatch)) ?
> + folios_put(&fbatch);
> }
> EXPORT_SYMBOL(release_pages);
>
