Messages in this thread | | | Date | Tue, 9 Apr 2024 09:34:28 +0200 | Subject | Re: [PATCH v7 2/7] mm: swap: free_swap_and_cache_nr() as batched free_swap_and_cache() | From | David Hildenbrand <> |
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On 08.04.24 20:39, Ryan Roberts wrote: > Now that we no longer have a convenient flag in the cluster to determine > if a folio is large, free_swap_and_cache() will take a reference and > lock a large folio much more often, which could lead to contention and > (e.g.) failure to split large folios, etc. > > Let's solve that problem by batch freeing swap and cache with a new > function, free_swap_and_cache_nr(), to free a contiguous range of swap > entries together. This allows us to first drop a reference to each swap > slot before we try to release the cache folio. This means we only try to > release the folio once, only taking the reference and lock once - much > better than the previous 512 times for the 2M THP case. > > Contiguous swap entries are gathered in zap_pte_range() and > madvise_free_pte_range() in a similar way to how present ptes are > already gathered in zap_pte_range(). > > While we are at it, let's simplify by converting the return type of both > functions to void. The return value was used only by zap_pte_range() to > print a bad pte, and was ignored by everyone else, so the extra > reporting wasn't exactly guaranteed. We will still get the warning with > most of the information from get_swap_device(). With the batch version, > we wouldn't know which pte was bad anyway so could print the wrong one. > > Signed-off-by: Ryan Roberts <ryan.roberts@arm.com> > --- > include/linux/pgtable.h | 29 ++++++++++++ > include/linux/swap.h | 12 +++-- > mm/internal.h | 63 ++++++++++++++++++++++++++ > mm/madvise.c | 12 +++-- > mm/memory.c | 13 +++--- > mm/swapfile.c | 97 +++++++++++++++++++++++++++++++++-------- > 6 files changed, 195 insertions(+), 31 deletions(-) > > diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h > index a3fc8150b047..75096025fe52 100644 > --- a/include/linux/pgtable.h > +++ b/include/linux/pgtable.h > @@ -708,6 +708,35 @@ static inline void pte_clear_not_present_full(struct mm_struct *mm, > } > #endif > > +#ifndef clear_not_present_full_ptes > +/** > + * clear_not_present_full_ptes - Clear multiple not present PTEs which are > + * consecutive in the pgtable. > + * @mm: Address space the ptes represent. > + * @addr: Address of the first pte. > + * @ptep: Page table pointer for the first entry. > + * @nr: Number of entries to clear. > + * @full: Whether we are clearing a full mm. > + * > + * May be overridden by the architecture; otherwise, implemented as a simple > + * loop over pte_clear_not_present_full(). > + * > + * Context: The caller holds the page table lock. The PTEs are all not present. > + * The PTEs are all in the same PMD. > + */ > +static inline void clear_not_present_full_ptes(struct mm_struct *mm, > + unsigned long addr, pte_t *ptep, unsigned int nr, int full) > +{ > + for (;;) { > + pte_clear_not_present_full(mm, addr, ptep, full); > + if (--nr == 0) > + break; > + ptep++; > + addr += PAGE_SIZE; > + } > +} > +#endif > + > #ifndef __HAVE_ARCH_PTEP_CLEAR_FLUSH > extern pte_t ptep_clear_flush(struct vm_area_struct *vma, > unsigned long address, > diff --git a/include/linux/swap.h b/include/linux/swap.h > index f6f78198f000..5737236dc3ce 100644 > --- a/include/linux/swap.h > +++ b/include/linux/swap.h > @@ -471,7 +471,7 @@ extern int swap_duplicate(swp_entry_t); > extern int swapcache_prepare(swp_entry_t); > extern void swap_free(swp_entry_t); > extern void swapcache_free_entries(swp_entry_t *entries, int n); > -extern int free_swap_and_cache(swp_entry_t); > +extern void free_swap_and_cache_nr(swp_entry_t entry, int nr); > int swap_type_of(dev_t device, sector_t offset); > int find_first_swap(dev_t *device); > extern unsigned int count_swap_pages(int, int); > @@ -520,8 +520,9 @@ static inline void put_swap_device(struct swap_info_struct *si) > #define free_pages_and_swap_cache(pages, nr) \ > release_pages((pages), (nr)); > > -/* used to sanity check ptes in zap_pte_range when CONFIG_SWAP=0 */ > -#define free_swap_and_cache(e) is_pfn_swap_entry(e) > +static inline void free_swap_and_cache_nr(swp_entry_t entry, int nr) > +{ > +} > > static inline void free_swap_cache(struct folio *folio) > { > @@ -589,6 +590,11 @@ static inline int add_swap_extent(struct swap_info_struct *sis, > } > #endif /* CONFIG_SWAP */ > > +static inline void free_swap_and_cache(swp_entry_t entry) > +{ > + free_swap_and_cache_nr(entry, 1); > +} > + > #ifdef CONFIG_MEMCG > static inline int mem_cgroup_swappiness(struct mem_cgroup *memcg) > { > diff --git a/mm/internal.h b/mm/internal.h > index 3bdc8693b54f..de68705624b0 100644 > --- a/mm/internal.h > +++ b/mm/internal.h > @@ -11,6 +11,8 @@ > #include <linux/mm.h> > #include <linux/pagemap.h> > #include <linux/rmap.h> > +#include <linux/swap.h> > +#include <linux/swapops.h> > #include <linux/tracepoint-defs.h> > > struct folio_batch; > @@ -189,6 +191,67 @@ static inline int folio_pte_batch(struct folio *folio, unsigned long addr, > > return min(ptep - start_ptep, max_nr); > } > + > +/** > + * pte_next_swp_offset - Increment the swap entry offset field of a swap pte. > + * @pte: The initial pte state; is_swap_pte(pte) must be true.
Likely we also want non_swap_entry() to be false.
> + * > + * Increments the swap offset, while maintaining all other fields, including > + * swap type, and any swp pte bits. The resulting pte is returned. > + */ > +static inline pte_t pte_next_swp_offset(pte_t pte) > +{ > + swp_entry_t entry = pte_to_swp_entry(pte); > + pte_t new = __swp_entry_to_pte(__swp_entry(swp_type(entry), > + swp_offset(entry) + 1)); > + > + if (pte_swp_soft_dirty(pte)) > + new = pte_swp_mksoft_dirty(new); > + if (pte_swp_exclusive(pte)) > + new = pte_swp_mkexclusive(new); > + if (pte_swp_uffd_wp(pte)) > + new = pte_swp_mkuffd_wp(new); > + > + return new; > +}
Acked-by: David Hildenbrand <david@redhat.com>
-- Cheers,
David / dhildenb
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