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Wed, 08 May 2024 00:49:36 -0700 (PDT) MIME-Version: 1.0 References: <20240502084609.28376-1-ryncsn@gmail.com> <20240502084939.30250-5-ryncsn@gmail.com> <874jb8lq8q.fsf@yhuang6-desk2.ccr.corp.intel.com> In-Reply-To: <874jb8lq8q.fsf@yhuang6-desk2.ccr.corp.intel.com> From: Kairui Song Date: Wed, 8 May 2024 15:49:20 +0800 Message-ID: Subject: Re: [PATCH v4 12/12] mm/swap: reduce swap cache search space To: "Huang, Ying" Cc: linux-mm@kvack.org, Andrew Morton , Matthew Wilcox , Chris Li , Barry Song , Ryan Roberts , Neil Brown , Minchan Kim , Hugh Dickins , David Hildenbrand , Yosry Ahmed , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: E461E140002 X-Stat-Signature: sdfnfci458o45dd4y9ep66nfb3p3ygei X-Rspam-User: X-HE-Tag: 1715154578-367516 X-HE-Meta: U2FsdGVkX1+Ur/Ldsbs5CqYgSJEBv5SW1kC6qSyV1ssSxnVRSdtGnqpD2ksIo+YaT+fXGKvSbwlqeDfsKKUq5ImUl2WWwwCSC48B5x9bVzEgs9O1UN89GQFsRFvnUGetmF8yIJLlfL4NbI80mNLH1efaZ3+teUU67IY0vVuRuSmYGwur2c4Dg6CC/trFdx9qT5eQxo9pYk3RdXht/uj5HrwO0GSKjjtZ371teCRCxk1nJiNnZr5iv4yhA9ihDOK5dGLbw1dF26i957UofjsX/Y+5JZgdHsKRFr0Ho9tOESg8XE3AtQcvt2BY97FCXSSB0kXmjdUghcY+bDnGuEHHXrMgpn6GSlyzfegq6hWybA4CXixCmitakJUvmpFxxlM71MnM1Uq/zAUoM+OVAYNgzX0p1lyA5Lbb1xEwuppKaOsohLaapKbRy0Zd3V6yXa+KnsyKQi+ozj3xfiWFzPMILQi4ld3IbYUuB7sQ0EumZK5dY2fCguPtKgMHsRnCQFzhROoAPumEf+dDRIrrdbupI+dXp90VenIrqkJewG7dNLC9WR2rSVmjX90zm9YDCaexljiNsjofY5nBaOWzKjvrEE72imhnF3BzmYawOofQHeRiICahyfZuokUYb0ohBGnnYOgy2DEMd8vceMPvWKUS+XVnl+Okt3Xqwmgl4WBsAz+qaxw8jR7uHQImLgag5wLal4lZ2ksA6m8dk/sMRTiB2npBd1hhWPTiC6DfIZmDEs3UZjs/FsnVcGDIq4e+DU9ZAItmtLWQ37kyk1+5QFN+rQk6+ueGpiYB37f9vUVPle4xCz0i00Ax9m09l6z5Mpfr0HQaxS3aRRgL3uAqbsFfrNeIib81R0FWLtnbwPj8mB5HhoNDlftOetD1hqJ8fo9q0jf6el3UY8oCNvVvb5PKCxfV6THooTh7wCaaHN3ID6nKjmek9mAK2FbMJVwJzf4jTT2yTb+bQuSdwpG74Vn 7NuFhaUP rvJzBwAy80hEtP227Nb2wzc+9SAvQWgGr6KF9TO24SJuMKqrRUxxQ4LuqSbOapCT6ZVyjd7OsZtZWkzqcrPYJZc1Pho9DKYONYB1u8Jo/J+7b3GfqCxdUitWcoffkovozFHakQrpFp3L+4TdgDZKy3+lOdJRZMVb9OhAxuAzIjj/ZNPNdT19AAF46gDYgSm4oLLR2UXwJvIQrxKBM9p/Xd16M8FCajMo969AWQOO7sBiPg0/lWkGmJ+poQo+Tbz9F9sWrJOW48yaQ32nGW4sOO1jNt3ezQLMHPuaWMrTWa5iB56WvboP8N+DhHlLII+JNJVsJbn35m17a40Hj6Kuzo7NuyDZh3oi78CsOU+7jwCQ8tfhH5FpuelwZn5vdtXwUicul0k/qgzimhQQNA3l/oNX4l2ldq9mKgZCfl2XeDDXCYkq9XXiipNIcN5jAhiZt11i1 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, May 8, 2024 at 3:27=E2=80=AFPM Huang, Ying w= rote: > > Kairui Song writes: > > > From: Kairui Song > > > > Currently we use one swap_address_space for every 64M chunk to reduce l= ock > > contention, this is like having a set of smaller swap files inside one > > swap device. But when doing swap cache look up or insert, we are > > still using the offset of the whole large swap device. This is OK for > > correctness, as the offset (key) is unique. > > > > But Xarray is specially optimized for small indexes, it creates the > > radix tree levels lazily to be just enough to fit the largest key > > stored in one Xarray. So we are wasting tree nodes unnecessarily. > > > > For 64M chunk it should only take at most 3 levels to contain everythin= g. it should only take at most 3 levels to contain everything. > > But if we are using the offset from the whole swap device, the offset (= key) > > value will be way beyond 64M, and so will the tree level. > > > > Optimize this by using a new helper swap_cache_index to get a swap > > entry's unique offset in its own 64M swap_address_space. > > > > I see a ~1% performance gain in benchmark and actual workload with > > high memory pressure. > > > > Test with `time memhog 128G` inside a 8G memcg using 128G swap (ramdisk > > with SWP_SYNCHRONOUS_IO dropped, tested 3 times, results are stable. Th= e > > test result is similar but the improvement is smaller if SWP_SYNCHRONOU= S_IO > > is enabled, as swap out path can never skip swap cache): > > > > Before: > > 6.07user 250.74system 4:17.26elapsed 99%CPU (0avgtext+0avgdata 8373376m= axresident)k > > 0inputs+0outputs (55major+33555018minor)pagefaults 0swaps > > > > After (1.8% faster): > > 6.08user 246.09system 4:12.58elapsed 99%CPU (0avgtext+0avgdata 8373248m= axresident)k > > 0inputs+0outputs (54major+33555027minor)pagefaults 0swaps > > > > Similar result with MySQL and sysbench using swap: > > Before: > > 94055.61 qps > > > > After (0.8% faster): > > 94834.91 qps > > > > Radix tree slab usage is also very slightly lower. > > > > Signed-off-by: Kairui Song > > --- > > mm/huge_memory.c | 2 +- > > mm/memcontrol.c | 2 +- > > mm/mincore.c | 2 +- > > mm/shmem.c | 2 +- > > mm/swap.h | 15 +++++++++++++++ > > mm/swap_state.c | 19 ++++++++++--------- > > mm/swapfile.c | 6 +++--- > > 7 files changed, 32 insertions(+), 16 deletions(-) > > > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > > index d35d526ed48f..45829cc049d2 100644 > > --- a/mm/huge_memory.c > > +++ b/mm/huge_memory.c > > @@ -2918,7 +2918,7 @@ static void __split_huge_page(struct page *page, = struct list_head *list, > > split_page_memcg(head, order, new_order); > > > > if (folio_test_anon(folio) && folio_test_swapcache(folio)) { > > - offset =3D swp_offset(folio->swap); > > + offset =3D swap_cache_index(folio->swap); > > swap_cache =3D swap_address_space(folio->swap); > > xa_lock(&swap_cache->i_pages); > > } > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > > index d11536ef59ef..81b005c459cb 100644 > > --- a/mm/memcontrol.c > > +++ b/mm/memcontrol.c > > @@ -6165,7 +6165,7 @@ static struct page *mc_handle_swap_pte(struct vm_= area_struct *vma, > > * Because swap_cache_get_folio() updates some statistics counter= , > > * we call find_get_page() with swapper_space directly. > > */ > > - page =3D find_get_page(swap_address_space(ent), swp_offset(ent)); > > + page =3D find_get_page(swap_address_space(ent), swap_cache_index(= ent)); > > entry->val =3D ent.val; > > > > return page; > > diff --git a/mm/mincore.c b/mm/mincore.c > > index dad3622cc963..e31cf1bde614 100644 > > --- a/mm/mincore.c > > +++ b/mm/mincore.c > > @@ -139,7 +139,7 @@ static int mincore_pte_range(pmd_t *pmd, unsigned l= ong addr, unsigned long end, > > } else { > > #ifdef CONFIG_SWAP > > *vec =3D mincore_page(swap_address_space(= entry), > > - swp_offset(entry)); > > + swap_cache_index(entr= y)); > > #else > > WARN_ON(1); > > *vec =3D 1; > > diff --git a/mm/shmem.c b/mm/shmem.c > > index fa2a0ed97507..326315c12feb 100644 > > --- a/mm/shmem.c > > +++ b/mm/shmem.c > > @@ -1756,7 +1756,7 @@ static int shmem_replace_folio(struct folio **fol= iop, gfp_t gfp, > > > > old =3D *foliop; > > entry =3D old->swap; > > - swap_index =3D swp_offset(entry); > > + swap_index =3D swap_cache_index(entry); > > swap_mapping =3D swap_address_space(entry); > > > > /* > > diff --git a/mm/swap.h b/mm/swap.h > > index 82023ab93205..93e3e1b58a7f 100644 > > --- a/mm/swap.h > > +++ b/mm/swap.h > > @@ -27,6 +27,7 @@ void __swap_writepage(struct folio *folio, struct wri= teback_control *wbc); > > /* One swap address space for each 64M swap space */ > > #define SWAP_ADDRESS_SPACE_SHIFT 14 > > #define SWAP_ADDRESS_SPACE_PAGES (1 << SWAP_ADDRESS_SPACE_SHIFT) > > +#define SWAP_ADDRESS_SPACE_MASK (BIT(SWAP_ADDRESS_SPACE_S= HIFT) - 1) > > #define SWAP_ADDRESS_SPACE_MASK (SWAP_ADDRESS_SPACE_PAGES - 1) > ? > > We can use BIT() in SWAP_ADDRESS_SPACE_PAGES definition. > I'll just use (SWAP_ADDRESS_SPACE_PAGES - 1) then, I was trying to make the changes minimal, but prefered the BIT macro, a trivial change. > > extern struct address_space *swapper_spaces[]; > > #define swap_address_space(entry) \ > > (&swapper_spaces[swp_type(entry)][swp_offset(entry) \ > > @@ -40,6 +41,15 @@ static inline loff_t swap_dev_pos(swp_entry_t entry) > > return ((loff_t)swp_offset(entry)) << PAGE_SHIFT; > > } > > > > +/* > > + * Return the swap cache index of the swap entry. > > + */ > > +static inline pgoff_t swap_cache_index(swp_entry_t entry) > > +{ > > + BUILD_BUG_ON((SWP_OFFSET_MASK | SWAP_ADDRESS_SPACE_MASK) !=3D SWP= _OFFSET_MASK); > > + return swp_offset(entry) & SWAP_ADDRESS_SPACE_MASK; > > +} > > + > > void show_swap_cache_info(void); > > bool add_to_swap(struct folio *folio); > > void *get_shadow_from_swap_cache(swp_entry_t entry); > > @@ -86,6 +96,11 @@ static inline struct address_space *swap_address_spa= ce(swp_entry_t entry) > > return NULL; > > } > > > > +static inline pgoff_t swap_cache_index(swp_entry_t entry) > > +{ > > + return 0; > > +} > > + > > static inline void show_swap_cache_info(void) > > { > > } > > diff --git a/mm/swap_state.c b/mm/swap_state.c > > index 642c30d8376c..09415d4c7843 100644 > > --- a/mm/swap_state.c > > +++ b/mm/swap_state.c > > @@ -72,7 +72,7 @@ void show_swap_cache_info(void) > > void *get_shadow_from_swap_cache(swp_entry_t entry) > > { > > struct address_space *address_space =3D swap_address_space(entry)= ; > > - pgoff_t idx =3D swp_offset(entry); > > + pgoff_t idx =3D swap_cache_index(entry); > > void *shadow; > > > > shadow =3D xa_load(&address_space->i_pages, idx); > > @@ -89,7 +89,7 @@ int add_to_swap_cache(struct folio *folio, swp_entry_= t entry, > > gfp_t gfp, void **shadowp) > > { > > struct address_space *address_space =3D swap_address_space(entry)= ; > > - pgoff_t idx =3D swp_offset(entry); > > + pgoff_t idx =3D swap_cache_index(entry); > > XA_STATE_ORDER(xas, &address_space->i_pages, idx, folio_order(fol= io)); > > unsigned long i, nr =3D folio_nr_pages(folio); > > void *old; > > @@ -144,7 +144,7 @@ void __delete_from_swap_cache(struct folio *folio, > > struct address_space *address_space =3D swap_address_space(entry)= ; > > int i; > > long nr =3D folio_nr_pages(folio); > > - pgoff_t idx =3D swp_offset(entry); > > + pgoff_t idx =3D swap_cache_index(entry); > > XA_STATE(xas, &address_space->i_pages, idx); > > > > xas_set_update(&xas, workingset_update_node); > > @@ -248,18 +248,19 @@ void delete_from_swap_cache(struct folio *folio) > > void clear_shadow_from_swap_cache(int type, unsigned long begin, > > unsigned long end) > > { > > - unsigned long curr =3D begin; > > + unsigned long curr =3D begin, offset; > > Better to rename "offset" as "index" to avoid confusion? Good idea. > > void *old; > > > > for (;;) { > > + offset =3D curr & SWAP_ADDRESS_SPACE_MASK; > > swp_entry_t entry =3D swp_entry(type, curr); > > struct address_space *address_space =3D swap_address_spac= e(entry); > > - XA_STATE(xas, &address_space->i_pages, curr); > > + XA_STATE(xas, &address_space->i_pages, offset); > > > > xas_set_update(&xas, workingset_update_node); > > > > xa_lock_irq(&address_space->i_pages); > > - xas_for_each(&xas, old, end) { > > + xas_for_each(&xas, old, offset + min(end - curr, SWAP_ADD= RESS_SPACE_PAGES)) { > > Is there a bug in the original code? It doesn't check SWAP_ADDRESS_SPACE= _PAGES. That's OK, if the (end - curr) goes above SWAP_ADDRESS_SPACE_PAGES, it means all content in current address_space needs to be purged. xas_for_each will stop after it iterated all content in the current address space. This is a bit hackish though. > > And should it be changed to > > xas_for_each(&xas, old, min(offset + end - curr, SWAP_ADDRESS_SPA= CE_PAGES)) It should be equivalent, as described above, but yeah, this looks cleaner. I'll use your suggested code. > ? > > > if (!xa_is_value(old)) > > continue; > > xas_store(&xas, NULL); > > @@ -350,7 +351,7 @@ struct folio *swap_cache_get_folio(swp_entry_t entr= y, > > { > > struct folio *folio; > > > > - folio =3D filemap_get_folio(swap_address_space(entry), swp_offset= (entry)); > > + folio =3D filemap_get_folio(swap_address_space(entry), swap_cache= _index(entry)); > > if (!IS_ERR(folio)) { > > bool vma_ra =3D swap_use_vma_readahead(); > > bool readahead; > > @@ -420,7 +421,7 @@ struct folio *filemap_get_incore_folio(struct addre= ss_space *mapping, > > si =3D get_swap_device(swp); > > if (!si) > > return ERR_PTR(-ENOENT); > > - index =3D swp_offset(swp); > > + index =3D swap_cache_index(swp); > > folio =3D filemap_get_folio(swap_address_space(swp), index); > > put_swap_device(si); > > return folio; > > @@ -447,7 +448,7 @@ struct folio *__read_swap_cache_async(swp_entry_t e= ntry, gfp_t gfp_mask, > > * that would confuse statistics. > > */ > > folio =3D filemap_get_folio(swap_address_space(entry), > > - swp_offset(entry)); > > + swap_cache_index(entry)); > > if (!IS_ERR(folio)) > > goto got_folio; > > > > diff --git a/mm/swapfile.c b/mm/swapfile.c > > index 0b0ae6e8c764..4f0e8b2ac8aa 100644 > > --- a/mm/swapfile.c > > +++ b/mm/swapfile.c > > @@ -142,7 +142,7 @@ static int __try_to_reclaim_swap(struct swap_info_s= truct *si, > > struct folio *folio; > > int ret =3D 0; > > > > - folio =3D filemap_get_folio(swap_address_space(entry), offset); > > + folio =3D filemap_get_folio(swap_address_space(entry), swap_cache= _index(entry)); > > if (IS_ERR(folio)) > > return 0; > > /* > > @@ -2158,7 +2158,7 @@ static int try_to_unuse(unsigned int type) > > (i =3D find_next_to_unuse(si, i)) !=3D 0) { > > > > entry =3D swp_entry(type, i); > > - folio =3D filemap_get_folio(swap_address_space(entry), i)= ; > > + folio =3D filemap_get_folio(swap_address_space(entry), sw= ap_cache_index(entry)); > > if (IS_ERR(folio)) > > continue; > > > > @@ -3476,7 +3476,7 @@ EXPORT_SYMBOL_GPL(swapcache_mapping); > > > > pgoff_t __folio_swap_cache_index(struct folio *folio) > > { > > - return swp_offset(folio->swap); > > + return swap_cache_index(folio->swap); > > } > > EXPORT_SYMBOL_GPL(__folio_swap_cache_index); Thanks for the suggestions! > > -- > Best Regards, > Huang, Ying