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Message-ID: <e8b737fd-6204-419d-0592-5441ea344704@suse.cz>
Date: Thu, 12 Jan 2023 11:31:49 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Lorenzo Stoakes <lstoakes@...il.com>, linux-mm@...ck.org,
Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel@...r.kernel.org
Cc: Matthew Wilcox <willy@...radead.org>,
Hugh Dickins <hughd@...gle.com>,
Liam Howlett <liam.howlett@...cle.com>,
William Kucharski <william.kucharski@...cle.com>,
Christian Brauner <brauner@...nel.org>,
Jonathan Corbet <corbet@....net>,
Mike Rapoport <rppt@...nel.org>,
Joel Fernandes <joel@...lfernandes.org>,
Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: Re: [PATCH v3 2/5] mm: mlock: use folios and a folio batch internally
On 12/26/22 09:44, Lorenzo Stoakes wrote:
> This brings mlock in line with the folio batches declared in mm/swap.c and
> makes the code more consistent across the two.
>
> The existing mechanism for identifying which operation each folio in the
> batch is undergoing is maintained, i.e. using the lower 2 bits of the
> struct folio address (previously struct page address). This should continue
> to function correctly as folios remain at least system word-aligned.
>
> All invoctions of mlock() pass either a non-compound page or the head of a
> THP-compound page and no tail pages need updating so this functionality
> works with struct folios being used internally rather than struct pages.
>
> In this patch the external interface is kept identical to before in order
> to maintain separation between patches in the series, using a rather
> awkward conversion from struct page to struct folio in relevant functions.
>
> However, this maintenance of the existing interface is intended to be
> temporary - the next patch in the series will update the interfaces to
> accept folios directly.
>
> Signed-off-by: Lorenzo Stoakes <lstoakes@...il.com>
Acked-by: Vlastimil Babka <vbabka@...e.cz>
with some nits:
> -static struct lruvec *__munlock_page(struct page *page, struct lruvec *lruvec)
> +static struct lruvec *__munlock_folio(struct folio *folio, struct lruvec *lruvec)
> {
> - int nr_pages = thp_nr_pages(page);
> + int nr_pages = folio_nr_pages(folio);
> bool isolated = false;
>
> - if (!TestClearPageLRU(page))
> + if (!folio_test_clear_lru(folio))
> goto munlock;
>
> isolated = true;
> - lruvec = folio_lruvec_relock_irq(page_folio(page), lruvec);
> + lruvec = folio_lruvec_relock_irq(folio, lruvec);
>
> - if (PageUnevictable(page)) {
> + if (folio_test_unevictable(folio)) {
> /* Then mlock_count is maintained, but might undercount */
> - if (page->mlock_count)
> - page->mlock_count--;
> - if (page->mlock_count)
> + if (folio->mlock_count)
> + folio->mlock_count--;
> + if (folio->mlock_count)
> goto out;
> }
> /* else assume that was the last mlock: reclaim will fix it if not */
>
> munlock:
> - if (TestClearPageMlocked(page)) {
> - __mod_zone_page_state(page_zone(page), NR_MLOCK, -nr_pages);
> - if (isolated || !PageUnevictable(page))
> + if (folio_test_clear_mlocked(folio)) {
> + zone_stat_mod_folio(folio, NR_MLOCK, -nr_pages);
AFAIK the 1:1 replacement would be __zone_stat_mod_folio(), this is stronger
thus not causing a bug, but unneccessary?
> + if (isolated || !folio_test_unevictable(folio))
> __count_vm_events(UNEVICTABLE_PGMUNLOCKED, nr_pages);
> else
> __count_vm_events(UNEVICTABLE_PGSTRANDED, nr_pages);
> }
>
> - /* page_evictable() has to be checked *after* clearing Mlocked */
> - if (isolated && PageUnevictable(page) && page_evictable(page)) {
> - del_page_from_lru_list(page, lruvec);
> - ClearPageUnevictable(page);
> - add_page_to_lru_list(page, lruvec);
> + /* folio_evictable() has to be checked *after* clearing Mlocked */
> + if (isolated && folio_test_unevictable(folio) && folio_evictable(folio)) {
> + lruvec_del_folio(lruvec, folio);
> + folio_clear_unevictable(folio);
> + lruvec_add_folio(lruvec, folio);
> __count_vm_events(UNEVICTABLE_PGRESCUED, nr_pages);
> }
> out:
> if (isolated)
> - SetPageLRU(page);
> + folio_set_lru(folio);
> return lruvec;
> }
>
> /*
> - * Flags held in the low bits of a struct page pointer on the mlock_pvec.
> + * Flags held in the low bits of a struct folio pointer on the mlock_fbatch.
> */
> #define LRU_PAGE 0x1
> #define NEW_PAGE 0x2
Should it be X_FOLIO now?
> -static inline struct page *mlock_lru(struct page *page)
> +static inline struct folio *mlock_lru(struct folio *folio)
> {
> - return (struct page *)((unsigned long)page + LRU_PAGE);
> + return (struct folio *)((unsigned long)folio + LRU_PAGE);
> }
>
> -static inline struct page *mlock_new(struct page *page)
> +static inline struct folio *mlock_new(struct folio *folio)
> {
> - return (struct page *)((unsigned long)page + NEW_PAGE);
> + return (struct folio *)((unsigned long)folio + NEW_PAGE);
> }
>
> /*
> - * mlock_pagevec() is derived from pagevec_lru_move_fn():
> - * perhaps that can make use of such page pointer flags in future,
> - * but for now just keep it for mlock. We could use three separate
> - * pagevecs instead, but one feels better (munlocking a full pagevec
> - * does not need to drain mlocking pagevecs first).
> + * mlock_folio_batch() is derived from folio_batch_move_lru(): perhaps that can
> + * make use of such page pointer flags in future, but for now just keep it for
^ folio?
> + * mlock. We could use three separate folio batches instead, but one feels
> + * better (munlocking a full folio batch does not need to drain mlocking folio
> + * batches first).
> */
> -static void mlock_pagevec(struct pagevec *pvec)
> +static void mlock_folio_batch(struct folio_batch *fbatch)
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