From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f200.google.com (mail-pf0-f200.google.com [209.85.192.200]) by kanga.kvack.org (Postfix) with ESMTP id 5394F6B025E for ; Mon, 9 Oct 2017 21:10:15 -0400 (EDT) Received: by mail-pf0-f200.google.com with SMTP id t63so28911453pfi.5 for ; Mon, 09 Oct 2017 18:10:15 -0700 (PDT) Received: from mga14.intel.com (mga14.intel.com. [192.55.52.115]) by mx.google.com with ESMTPS id d22si8171282pli.461.2017.10.09.18.10.13 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 09 Oct 2017 18:10:14 -0700 (PDT) From: "Huang\, Ying" Subject: Re: [PATCH v2 4/4] mm:swap: skip swapcache for swapin of synchronous device References: <1505886205-9671-1-git-send-email-minchan@kernel.org> <1505886205-9671-5-git-send-email-minchan@kernel.org> <20171010003432.GA23073@bbox> Date: Tue, 10 Oct 2017 09:10:10 +0800 In-Reply-To: <20171010003432.GA23073@bbox> (Minchan Kim's message of "Tue, 10 Oct 2017 09:34:32 +0900") Message-ID: <874lr7q03x.fsf@yhuang-dev.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ascii Sender: owner-linux-mm@kvack.org List-ID: To: Minchan Kim Cc: huang ying , Andrew Morton , linux-mm@kvack.org, LKML , kernel-team , Christoph Hellwig , Dan Williams , Ross Zwisler , Hugh Dickins , Huang Ying Minchan Kim writes: > Hi Huang, > > Sorry for the late response. It was long national holiday. > > On Fri, Sep 29, 2017 at 04:51:17PM +0800, huang ying wrote: >> On Wed, Sep 20, 2017 at 1:43 PM, Minchan Kim wrote: >> > With fast swap storage, platform want to use swap more aggressively >> > and swap-in is crucial to application latency. >> > >> > The rw_page based synchronous devices like zram, pmem and btt are such >> > fast storage. When I profile swapin performance with zram lz4 decompress >> > test, S/W overhead is more than 70%. Maybe, it would be bigger in nvdimm. >> > >> > This patch aims for reducing swap-in latency via skipping swapcache >> > if swap device is synchronous device like rw_page based device. >> > It enhances 45% my swapin test(5G sequential swapin, no readahead, >> > from 2.41sec to 1.64sec). >> > >> > Cc: Dan Williams >> > Cc: Ross Zwisler >> > Cc: Hugh Dickins >> > Signed-off-by: Minchan Kim >> > --- >> > include/linux/swap.h | 11 +++++++++++ >> > mm/memory.c | 52 ++++++++++++++++++++++++++++++++++++---------------- >> > mm/page_io.c | 6 +++--- >> > mm/swapfile.c | 11 +++++++---- >> > 4 files changed, 57 insertions(+), 23 deletions(-) >> > >> > diff --git a/include/linux/swap.h b/include/linux/swap.h >> > index fbb33919d1c6..cd2f66fdfc2d 100644 >> > --- a/include/linux/swap.h >> > +++ b/include/linux/swap.h >> > @@ -461,6 +461,7 @@ extern int page_swapcount(struct page *); >> > extern int __swp_swapcount(swp_entry_t entry); >> > extern int swp_swapcount(swp_entry_t entry); >> > extern struct swap_info_struct *page_swap_info(struct page *); >> > +extern struct swap_info_struct *swp_swap_info(swp_entry_t entry); >> > extern bool reuse_swap_page(struct page *, int *); >> > extern int try_to_free_swap(struct page *); >> > struct backing_dev_info; >> > @@ -469,6 +470,16 @@ extern void exit_swap_address_space(unsigned int type); >> > >> > #else /* CONFIG_SWAP */ >> > >> > +static inline int swap_readpage(struct page *page, bool do_poll) >> > +{ >> > + return 0; >> > +} >> > + >> > +static inline struct swap_info_struct *swp_swap_info(swp_entry_t entry) >> > +{ >> > + return NULL; >> > +} >> > + >> > #define swap_address_space(entry) (NULL) >> > #define get_nr_swap_pages() 0L >> > #define total_swap_pages 0L >> > diff --git a/mm/memory.c b/mm/memory.c >> > index ec4e15494901..163ab2062385 100644 >> > --- a/mm/memory.c >> > +++ b/mm/memory.c >> > @@ -2842,7 +2842,7 @@ EXPORT_SYMBOL(unmap_mapping_range); >> > int do_swap_page(struct vm_fault *vmf) >> > { >> > struct vm_area_struct *vma = vmf->vma; >> > - struct page *page = NULL, *swapcache; >> > + struct page *page = NULL, *swapcache = NULL; >> > struct mem_cgroup *memcg; >> > struct vma_swap_readahead swap_ra; >> > swp_entry_t entry; >> > @@ -2881,17 +2881,35 @@ int do_swap_page(struct vm_fault *vmf) >> > } >> > goto out; >> > } >> > + >> > + >> > delayacct_set_flag(DELAYACCT_PF_SWAPIN); >> > if (!page) >> > page = lookup_swap_cache(entry, vma_readahead ? vma : NULL, >> > vmf->address); >> > if (!page) { >> > - if (vma_readahead) >> > - page = do_swap_page_readahead(entry, >> > - GFP_HIGHUSER_MOVABLE, vmf, &swap_ra); >> > - else >> > - page = swapin_readahead(entry, >> > - GFP_HIGHUSER_MOVABLE, vma, vmf->address); >> > + struct swap_info_struct *si = swp_swap_info(entry); >> > + >> > + if (!(si->flags & SWP_SYNCHRONOUS_IO)) { >> > + if (vma_readahead) >> > + page = do_swap_page_readahead(entry, >> > + GFP_HIGHUSER_MOVABLE, vmf, &swap_ra); >> > + else >> > + page = swapin_readahead(entry, >> > + GFP_HIGHUSER_MOVABLE, vma, vmf->address); >> > + swapcache = page; >> > + } else { >> > + /* skip swapcache */ >> > + page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, vmf->address); >> > + if (page) { >> > + __SetPageLocked(page); >> > + __SetPageSwapBacked(page); >> > + set_page_private(page, entry.val); >> > + lru_cache_add_anon(page); >> > + swap_readpage(page, true); >> > + } >> > + } >> >> I have a question for this. If a page is mapped in multiple processes >> (for example, because of fork). With swap cache, after swapping out >> and swapping in, the page will be still shared by these processes. >> But with your changes, it appears that there will be multiple pages >> with same contents mapped in multiple processes, even if the page >> isn't written in these processes. So this may waste some memory in >> some situation? And copying from device is even faster than looking >> up swap cache in your system? > > I expected a page shared by several processes has low possibility to swap out > compared to a single mapped page. Nonetheless, once it is swapped out, it also > has low chance to swap in so I didn't cover the case intentionally until we > get any regression report. Thanks for explanation. > However, a fix would be simple so I don't care to add up it. > Any thoughts? I think the fix can work well with shared anonymous pages in most cases (although not all). It should be good to add it. Best Regards, Huang, Ying > diff --git a/include/linux/swap.h b/include/linux/swap.h > index cd2f66fdfc2d..23f19ffa5cc3 100644 > --- a/include/linux/swap.h > +++ b/include/linux/swap.h > @@ -458,6 +458,7 @@ extern unsigned int count_swap_pages(int, int); > extern sector_t map_swap_page(struct page *, struct block_device **); > extern sector_t swapdev_block(int, pgoff_t); > extern int page_swapcount(struct page *); > +extern int __swap_count(struct swap_info_struct *si, swp_entry_t entry); > extern int __swp_swapcount(swp_entry_t entry); > extern int swp_swapcount(swp_entry_t entry); > extern struct swap_info_struct *page_swap_info(struct page *); > @@ -584,6 +585,11 @@ static inline int page_swapcount(struct page *page) > return 0; > } > > +static inline int __swap_count(structd swap_info_struct *si, swp_entry_t entry) > +{ > + return 0; > +} > + > static inline int __swp_swapcount(swp_entry_t entry) > { > return 0; > diff --git a/include/linux/swapfile.h b/include/linux/swapfile.h > index 388293a91e8c..49f8e19dd506 100644 > --- a/include/linux/swapfile.h > +++ b/include/linux/swapfile.h > @@ -9,5 +9,4 @@ extern spinlock_t swap_lock; > extern struct plist_head swap_active_head; > extern struct swap_info_struct *swap_info[]; > extern int try_to_unuse(unsigned int, bool, unsigned long); > - > #endif /* _LINUX_SWAPFILE_H */ > diff --git a/mm/memory.c b/mm/memory.c > index 163ab2062385..c6f0abe8b39b 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -2890,15 +2890,8 @@ int do_swap_page(struct vm_fault *vmf) > if (!page) { > struct swap_info_struct *si = swp_swap_info(entry); > > - if (!(si->flags & SWP_SYNCHRONOUS_IO)) { > - if (vma_readahead) > - page = do_swap_page_readahead(entry, > - GFP_HIGHUSER_MOVABLE, vmf, &swap_ra); > - else > - page = swapin_readahead(entry, > - GFP_HIGHUSER_MOVABLE, vma, vmf->address); > - swapcache = page; > - } else { > + if ((si->flags & SWP_SYNCHRONOUS_IO) && (vmf->flags & FAULT_FLAG_WRITE || > + __swap_count(si, entry) == 1)) { > /* skip swapcache */ > page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, vmf->address); > if (page) { > @@ -2908,6 +2901,14 @@ int do_swap_page(struct vm_fault *vmf) > lru_cache_add_anon(page); > swap_readpage(page, true); > } > + } else { > + if (vma_readahead) > + page = do_swap_page_readahead(entry, > + GFP_HIGHUSER_MOVABLE, vmf, &swap_ra); > + else > + page = swapin_readahead(entry, > + GFP_HIGHUSER_MOVABLE, vma, vmf->address); > + swapcache = page; > } > > if (!page) { > diff --git a/mm/swapfile.c b/mm/swapfile.c > index 64a3d85226ba..37d7ba71a2ca 100644 > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -1328,7 +1328,13 @@ int page_swapcount(struct page *page) > return count; > } > > -static int swap_swapcount(struct swap_info_struct *si, swp_entry_t entry) > +int __swap_count(struct swap_info_struct *si, swp_entry_t entry) > +{ > + pgoff_t offset = swp_offset(entry); > + return swap_count(si->swap_map[offset]); > +} > + > +int swap_swapcount(struct swap_info_struct *si, swp_entry_t entry) > { > int count = 0; > pgoff_t offset = swp_offset(entry); -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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