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SubjectRe: [PATCH v2 1/5] mm: swap: introduce swap_free_nr() for batched swap_free()
Ryan Roberts <ryan.roberts@arm.com> 于2024年4月11日周四 22:30写道:
>
> On 09/04/2024 09:26, Barry Song wrote:
> > From: Chuanhua Han <hanchuanhua@oppo.com>
> >
> > While swapping in a large folio, we need to free swaps related to the whole
> > folio. To avoid frequently acquiring and releasing swap locks, it is better
> > to introduce an API for batched free.
> >
> > Signed-off-by: Chuanhua Han <hanchuanhua@oppo.com>
> > Co-developed-by: Barry Song <v-songbaohua@oppo.com>
> > Signed-off-by: Barry Song <v-songbaohua@oppo.com>
>
> Couple of nits; feel free to ignore.
>
> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
>
> > ---
> > include/linux/swap.h | 5 +++++
> > mm/swapfile.c | 51 ++++++++++++++++++++++++++++++++++++++++++++
> > 2 files changed, 56 insertions(+)
> >
> > diff --git a/include/linux/swap.h b/include/linux/swap.h
> > index 11c53692f65f..b7a107e983b8 100644
> > --- a/include/linux/swap.h
> > +++ b/include/linux/swap.h
> > @@ -483,6 +483,7 @@ extern void swap_shmem_alloc(swp_entry_t);
> > extern int swap_duplicate(swp_entry_t);
> > extern int swapcache_prepare(swp_entry_t);
> > extern void swap_free(swp_entry_t);
> > +extern void swap_free_nr(swp_entry_t entry, int nr_pages);
> > extern void swapcache_free_entries(swp_entry_t *entries, int n);
> > extern void free_swap_and_cache_nr(swp_entry_t entry, int nr);
> > int swap_type_of(dev_t device, sector_t offset);
> > @@ -564,6 +565,10 @@ static inline void swap_free(swp_entry_t swp)
> > {
> > }
> >
> > +void swap_free_nr(swp_entry_t entry, int nr_pages)
> > +{
> > +}
> > +
> > static inline void put_swap_folio(struct folio *folio, swp_entry_t swp)
> > {
> > }
> > diff --git a/mm/swapfile.c b/mm/swapfile.c
> > index 28642c188c93..f4c65aeb088d 100644
> > --- a/mm/swapfile.c
> > +++ b/mm/swapfile.c
> > @@ -1356,6 +1356,57 @@ void swap_free(swp_entry_t entry)
> > __swap_entry_free(p, entry);
> > }
> >
> > +/*
> > + * Free up the maximum number of swap entries at once to limit the
> > + * maximum kernel stack usage.
> > + */
> > +#define SWAP_BATCH_NR (SWAPFILE_CLUSTER > 512 ? 512 : SWAPFILE_CLUSTER)
> > +
> > +/*
> > + * Called after swapping in a large folio, batched free swap entries
> > + * for this large folio, entry should be for the first subpage and
> > + * its offset is aligned with nr_pages
> > + */
> > +void swap_free_nr(swp_entry_t entry, int nr_pages)
> > +{
> > + int i, j;
> > + struct swap_cluster_info *ci;
> > + struct swap_info_struct *p;
> > + unsigned int type = swp_type(entry);
> > + unsigned long offset = swp_offset(entry);
> > + int batch_nr, remain_nr;
> > + DECLARE_BITMAP(usage, SWAP_BATCH_NR) = { 0 };
> > +
> > + /* all swap entries are within a cluster for mTHP */
> > + VM_BUG_ON(offset % SWAPFILE_CLUSTER + nr_pages > SWAPFILE_CLUSTER);
> > +
> > + if (nr_pages == 1) {
> > + swap_free(entry);
> > + return;
> > + }
> > +
> > + remain_nr = nr_pages;
> > + p = _swap_info_get(entry);
> > + if (p) {
>
> nit: perhaps return early if (!p) ? Then you dedent the for() block.

Agreed!

>
> > + for (i = 0; i < nr_pages; i += batch_nr) {
> > + batch_nr = min_t(int, SWAP_BATCH_NR, remain_nr);
> > +
> > + ci = lock_cluster_or_swap_info(p, offset);
> > + for (j = 0; j < batch_nr; j++) {
> > + if (__swap_entry_free_locked(p, offset + i * SWAP_BATCH_NR + j, 1))
> > + __bitmap_set(usage, j, 1);
> > + }
> > + unlock_cluster_or_swap_info(p, ci);
> > +
> > + for_each_clear_bit(j, usage, batch_nr)
> > + free_swap_slot(swp_entry(type, offset + i * SWAP_BATCH_NR + j));
> > +
>
> nit: perhaps change to for (;;), and do the checks here to avoid clearing the
> bitmap on the last run:
>
> i += batch_nr;
> if (i < nr_pages)
> break;
Great, thank you for your advice!
>
> > + bitmap_clear(usage, 0, SWAP_BATCH_NR);
> > + remain_nr -= batch_nr;
> > + }
> > + }
> > +}
> > +
> > /*
> > * Called after dropping swapcache to decrease refcnt to swap entries.
> > */
>
>


--
Thanks,
Chuanhua

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