| Message ID | 20240327144537.4165578-2-ryan.roberts@arm.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Swap-out mTHP without splitting | expand |
Ryan Roberts <ryan.roberts@arm.com> writes: > As preparation for supporting small-sized THP in the swap-out path, > without first needing to split to order-0, Remove the CLUSTER_FLAG_HUGE, > which, when present, always implies PMD-sized THP, which is the same as > the cluster size. > > The only use of the flag was to determine whether a swap entry refers to > a single page or a PMD-sized THP in swap_page_trans_huge_swapped(). > Instead of relying on the flag, we now pass in nr_pages, which > originates from the folio's number of pages. This allows the logic to > work for folios of any order. > > The one snag is that one of the swap_page_trans_huge_swapped() call > sites does not have the folio. But it was only being called there to > shortcut a call __try_to_reclaim_swap() in some cases. > __try_to_reclaim_swap() gets the folio and (via some other functions) > calls swap_page_trans_huge_swapped(). So I've removed the problematic > call site and believe the new logic should be functionally equivalent. > > That said, removing the fast path means that we will take a reference > and trylock a large folio much more often, which we would like to avoid. > The next patch will solve this. > > Removing CLUSTER_FLAG_HUGE also means we can remove split_swap_cluster() > which used to be called during folio splitting, since > split_swap_cluster()'s only job was to remove the flag. > > Signed-off-by: Ryan Roberts <ryan.roberts@arm.com> LGTM, Thanks! Reviewed-by: "Huang, Ying" <ying.huang@intel.com> > --- > include/linux/swap.h | 10 ---------- > mm/huge_memory.c | 3 --- > mm/swapfile.c | 47 ++++++++------------------------------------ > 3 files changed, 8 insertions(+), 52 deletions(-) > > diff --git a/include/linux/swap.h b/include/linux/swap.h > index a211a0383425..f6f78198f000 100644 > --- a/include/linux/swap.h > +++ b/include/linux/swap.h > @@ -259,7 +259,6 @@ struct swap_cluster_info { > }; > #define CLUSTER_FLAG_FREE 1 /* This cluster is free */ > #define CLUSTER_FLAG_NEXT_NULL 2 /* This cluster has no next cluster */ > -#define CLUSTER_FLAG_HUGE 4 /* This cluster is backing a transparent huge page */ > > /* > * We assign a cluster to each CPU, so each CPU can allocate swap entry from > @@ -590,15 +589,6 @@ static inline int add_swap_extent(struct swap_info_struct *sis, > } > #endif /* CONFIG_SWAP */ > > -#ifdef CONFIG_THP_SWAP > -extern int split_swap_cluster(swp_entry_t entry); > -#else > -static inline int split_swap_cluster(swp_entry_t entry) > -{ > - return 0; > -} > -#endif > - > #ifdef CONFIG_MEMCG > static inline int mem_cgroup_swappiness(struct mem_cgroup *memcg) > { > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index b49fcb8a16cc..8c1f3393994a 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -2961,9 +2961,6 @@ static void __split_huge_page(struct page *page, struct list_head *list, > shmem_uncharge(folio->mapping->host, nr_dropped); > remap_page(folio, nr); > > - if (folio_test_swapcache(folio)) > - split_swap_cluster(folio->swap); > - > /* > * set page to its compound_head when split to non order-0 pages, so > * we can skip unlocking it below, since PG_locked is transferred to > diff --git a/mm/swapfile.c b/mm/swapfile.c > index 5e6d2304a2a4..0d44ee2b4f9c 100644 > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -343,18 +343,6 @@ static inline void cluster_set_null(struct swap_cluster_info *info) > info->data = 0; > } > > -static inline bool cluster_is_huge(struct swap_cluster_info *info) > -{ > - if (IS_ENABLED(CONFIG_THP_SWAP)) > - return info->flags & CLUSTER_FLAG_HUGE; > - return false; > -} > - > -static inline void cluster_clear_huge(struct swap_cluster_info *info) > -{ > - info->flags &= ~CLUSTER_FLAG_HUGE; > -} > - > static inline struct swap_cluster_info *lock_cluster(struct swap_info_struct *si, > unsigned long offset) > { > @@ -1027,7 +1015,7 @@ static int swap_alloc_cluster(struct swap_info_struct *si, swp_entry_t *slot) > offset = idx * SWAPFILE_CLUSTER; > ci = lock_cluster(si, offset); > alloc_cluster(si, idx); > - cluster_set_count_flag(ci, SWAPFILE_CLUSTER, CLUSTER_FLAG_HUGE); > + cluster_set_count(ci, SWAPFILE_CLUSTER); > > memset(si->swap_map + offset, SWAP_HAS_CACHE, SWAPFILE_CLUSTER); > unlock_cluster(ci); > @@ -1365,7 +1353,6 @@ void put_swap_folio(struct folio *folio, swp_entry_t entry) > > ci = lock_cluster_or_swap_info(si, offset); > if (size == SWAPFILE_CLUSTER) { > - VM_BUG_ON(!cluster_is_huge(ci)); > map = si->swap_map + offset; > for (i = 0; i < SWAPFILE_CLUSTER; i++) { > val = map[i]; > @@ -1373,7 +1360,6 @@ void put_swap_folio(struct folio *folio, swp_entry_t entry) > if (val == SWAP_HAS_CACHE) > free_entries++; > } > - cluster_clear_huge(ci); > if (free_entries == SWAPFILE_CLUSTER) { > unlock_cluster_or_swap_info(si, ci); > spin_lock(&si->lock); > @@ -1395,23 +1381,6 @@ void put_swap_folio(struct folio *folio, swp_entry_t entry) > unlock_cluster_or_swap_info(si, ci); > } > > -#ifdef CONFIG_THP_SWAP > -int split_swap_cluster(swp_entry_t entry) > -{ > - struct swap_info_struct *si; > - struct swap_cluster_info *ci; > - unsigned long offset = swp_offset(entry); > - > - si = _swap_info_get(entry); > - if (!si) > - return -EBUSY; > - ci = lock_cluster(si, offset); > - cluster_clear_huge(ci); > - unlock_cluster(ci); > - return 0; > -} > -#endif > - > static int swp_entry_cmp(const void *ent1, const void *ent2) > { > const swp_entry_t *e1 = ent1, *e2 = ent2; > @@ -1519,22 +1488,23 @@ int swp_swapcount(swp_entry_t entry) > } > > static bool swap_page_trans_huge_swapped(struct swap_info_struct *si, > - swp_entry_t entry) > + swp_entry_t entry, > + unsigned int nr_pages) > { > struct swap_cluster_info *ci; > unsigned char *map = si->swap_map; > unsigned long roffset = swp_offset(entry); > - unsigned long offset = round_down(roffset, SWAPFILE_CLUSTER); > + unsigned long offset = round_down(roffset, nr_pages); > int i; > bool ret = false; > > ci = lock_cluster_or_swap_info(si, offset); > - if (!ci || !cluster_is_huge(ci)) { > + if (!ci || nr_pages == 1) { > if (swap_count(map[roffset])) > ret = true; > goto unlock_out; > } > - for (i = 0; i < SWAPFILE_CLUSTER; i++) { > + for (i = 0; i < nr_pages; i++) { > if (swap_count(map[offset + i])) { > ret = true; > break; > @@ -1556,7 +1526,7 @@ static bool folio_swapped(struct folio *folio) > if (!IS_ENABLED(CONFIG_THP_SWAP) || likely(!folio_test_large(folio))) > return swap_swapcount(si, entry) != 0; > > - return swap_page_trans_huge_swapped(si, entry); > + return swap_page_trans_huge_swapped(si, entry, folio_nr_pages(folio)); > } > > /** > @@ -1622,8 +1592,7 @@ int free_swap_and_cache(swp_entry_t entry) > } > > count = __swap_entry_free(p, entry); > - if (count == SWAP_HAS_CACHE && > - !swap_page_trans_huge_swapped(p, entry)) > + if (count == SWAP_HAS_CACHE) > __try_to_reclaim_swap(p, swp_offset(entry), > TTRS_UNMAPPED | TTRS_FULL); > put_swap_device(p);
On 27.03.24 15:45, Ryan Roberts wrote: > As preparation for supporting small-sized THP in the swap-out path, > without first needing to split to order-0, Remove the CLUSTER_FLAG_HUGE, > which, when present, always implies PMD-sized THP, which is the same as > the cluster size. > > The only use of the flag was to determine whether a swap entry refers to > a single page or a PMD-sized THP in swap_page_trans_huge_swapped(). > Instead of relying on the flag, we now pass in nr_pages, which > originates from the folio's number of pages. This allows the logic to > work for folios of any order. > > The one snag is that one of the swap_page_trans_huge_swapped() call > sites does not have the folio. But it was only being called there to > shortcut a call __try_to_reclaim_swap() in some cases. > __try_to_reclaim_swap() gets the folio and (via some other functions) > calls swap_page_trans_huge_swapped(). So I've removed the problematic > call site and believe the new logic should be functionally equivalent. > > That said, removing the fast path means that we will take a reference > and trylock a large folio much more often, which we would like to avoid. > The next patch will solve this. > > Removing CLUSTER_FLAG_HUGE also means we can remove split_swap_cluster() > which used to be called during folio splitting, since > split_swap_cluster()'s only job was to remove the flag. > > Signed-off-by: Ryan Roberts <ryan.roberts@arm.com> > --- Looks like a reasonable cleanup independent of everything else Acked-by: David Hildenbrand <david@redhat.com>
diff --git a/include/linux/swap.h b/include/linux/swap.h index a211a0383425..f6f78198f000 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -259,7 +259,6 @@ struct swap_cluster_info { }; #define CLUSTER_FLAG_FREE 1 /* This cluster is free */ #define CLUSTER_FLAG_NEXT_NULL 2 /* This cluster has no next cluster */ -#define CLUSTER_FLAG_HUGE 4 /* This cluster is backing a transparent huge page */ /* * We assign a cluster to each CPU, so each CPU can allocate swap entry from @@ -590,15 +589,6 @@ static inline int add_swap_extent(struct swap_info_struct *sis, } #endif /* CONFIG_SWAP */ -#ifdef CONFIG_THP_SWAP -extern int split_swap_cluster(swp_entry_t entry); -#else -static inline int split_swap_cluster(swp_entry_t entry) -{ - return 0; -} -#endif - #ifdef CONFIG_MEMCG static inline int mem_cgroup_swappiness(struct mem_cgroup *memcg) { diff --git a/mm/huge_memory.c b/mm/huge_memory.c index b49fcb8a16cc..8c1f3393994a 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2961,9 +2961,6 @@ static void __split_huge_page(struct page *page, struct list_head *list, shmem_uncharge(folio->mapping->host, nr_dropped); remap_page(folio, nr); - if (folio_test_swapcache(folio)) - split_swap_cluster(folio->swap); - /* * set page to its compound_head when split to non order-0 pages, so * we can skip unlocking it below, since PG_locked is transferred to diff --git a/mm/swapfile.c b/mm/swapfile.c index 5e6d2304a2a4..0d44ee2b4f9c 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -343,18 +343,6 @@ static inline void cluster_set_null(struct swap_cluster_info *info) info->data = 0; } -static inline bool cluster_is_huge(struct swap_cluster_info *info) -{ - if (IS_ENABLED(CONFIG_THP_SWAP)) - return info->flags & CLUSTER_FLAG_HUGE; - return false; -} - -static inline void cluster_clear_huge(struct swap_cluster_info *info) -{ - info->flags &= ~CLUSTER_FLAG_HUGE; -} - static inline struct swap_cluster_info *lock_cluster(struct swap_info_struct *si, unsigned long offset) { @@ -1027,7 +1015,7 @@ static int swap_alloc_cluster(struct swap_info_struct *si, swp_entry_t *slot) offset = idx * SWAPFILE_CLUSTER; ci = lock_cluster(si, offset); alloc_cluster(si, idx); - cluster_set_count_flag(ci, SWAPFILE_CLUSTER, CLUSTER_FLAG_HUGE); + cluster_set_count(ci, SWAPFILE_CLUSTER); memset(si->swap_map + offset, SWAP_HAS_CACHE, SWAPFILE_CLUSTER); unlock_cluster(ci); @@ -1365,7 +1353,6 @@ void put_swap_folio(struct folio *folio, swp_entry_t entry) ci = lock_cluster_or_swap_info(si, offset); if (size == SWAPFILE_CLUSTER) { - VM_BUG_ON(!cluster_is_huge(ci)); map = si->swap_map + offset; for (i = 0; i < SWAPFILE_CLUSTER; i++) { val = map[i]; @@ -1373,7 +1360,6 @@ void put_swap_folio(struct folio *folio, swp_entry_t entry) if (val == SWAP_HAS_CACHE) free_entries++; } - cluster_clear_huge(ci); if (free_entries == SWAPFILE_CLUSTER) { unlock_cluster_or_swap_info(si, ci); spin_lock(&si->lock); @@ -1395,23 +1381,6 @@ void put_swap_folio(struct folio *folio, swp_entry_t entry) unlock_cluster_or_swap_info(si, ci); } -#ifdef CONFIG_THP_SWAP -int split_swap_cluster(swp_entry_t entry) -{ - struct swap_info_struct *si; - struct swap_cluster_info *ci; - unsigned long offset = swp_offset(entry); - - si = _swap_info_get(entry); - if (!si) - return -EBUSY; - ci = lock_cluster(si, offset); - cluster_clear_huge(ci); - unlock_cluster(ci); - return 0; -} -#endif - static int swp_entry_cmp(const void *ent1, const void *ent2) { const swp_entry_t *e1 = ent1, *e2 = ent2; @@ -1519,22 +1488,23 @@ int swp_swapcount(swp_entry_t entry) } static bool swap_page_trans_huge_swapped(struct swap_info_struct *si, - swp_entry_t entry) + swp_entry_t entry, + unsigned int nr_pages) { struct swap_cluster_info *ci; unsigned char *map = si->swap_map; unsigned long roffset = swp_offset(entry); - unsigned long offset = round_down(roffset, SWAPFILE_CLUSTER); + unsigned long offset = round_down(roffset, nr_pages); int i; bool ret = false; ci = lock_cluster_or_swap_info(si, offset); - if (!ci || !cluster_is_huge(ci)) { + if (!ci || nr_pages == 1) { if (swap_count(map[roffset])) ret = true; goto unlock_out; } - for (i = 0; i < SWAPFILE_CLUSTER; i++) { + for (i = 0; i < nr_pages; i++) { if (swap_count(map[offset + i])) { ret = true; break; @@ -1556,7 +1526,7 @@ static bool folio_swapped(struct folio *folio) if (!IS_ENABLED(CONFIG_THP_SWAP) || likely(!folio_test_large(folio))) return swap_swapcount(si, entry) != 0; - return swap_page_trans_huge_swapped(si, entry); + return swap_page_trans_huge_swapped(si, entry, folio_nr_pages(folio)); } /** @@ -1622,8 +1592,7 @@ int free_swap_and_cache(swp_entry_t entry) } count = __swap_entry_free(p, entry); - if (count == SWAP_HAS_CACHE && - !swap_page_trans_huge_swapped(p, entry)) + if (count == SWAP_HAS_CACHE) __try_to_reclaim_swap(p, swp_offset(entry), TTRS_UNMAPPED | TTRS_FULL); put_swap_device(p);
As preparation for supporting small-sized THP in the swap-out path, without first needing to split to order-0, Remove the CLUSTER_FLAG_HUGE, which, when present, always implies PMD-sized THP, which is the same as the cluster size. The only use of the flag was to determine whether a swap entry refers to a single page or a PMD-sized THP in swap_page_trans_huge_swapped(). Instead of relying on the flag, we now pass in nr_pages, which originates from the folio's number of pages. This allows the logic to work for folios of any order. The one snag is that one of the swap_page_trans_huge_swapped() call sites does not have the folio. But it was only being called there to shortcut a call __try_to_reclaim_swap() in some cases. __try_to_reclaim_swap() gets the folio and (via some other functions) calls swap_page_trans_huge_swapped(). So I've removed the problematic call site and believe the new logic should be functionally equivalent. That said, removing the fast path means that we will take a reference and trylock a large folio much more often, which we would like to avoid. The next patch will solve this. Removing CLUSTER_FLAG_HUGE also means we can remove split_swap_cluster() which used to be called during folio splitting, since split_swap_cluster()'s only job was to remove the flag. Signed-off-by: Ryan Roberts <ryan.roberts@arm.com> --- include/linux/swap.h | 10 ---------- mm/huge_memory.c | 3 --- mm/swapfile.c | 47 ++++++++------------------------------------ 3 files changed, 8 insertions(+), 52 deletions(-)