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Date: Wed, 01 Nov 2017 13:41:00 +0800
From: "Huang\, Ying" <ying.huang@...el.com>
To: Minchan Kim <minchan@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
Hugh Dickins <hughd@...gle.com>,
Huang Ying <ying.huang@...el.com>,
kernel-team <kernel-team@....com>
Subject: Re: [PATCH 1/2] mm:swap: clean up swap readahead
Hi, Minchan,
Minchan Kim <minchan@...nel.org> writes:
> When I see recent change of swap readahead, I am very unhappy
> about current code structure which diverges two swap readahead
> algorithm in do_swap_page. This patch is to clean it up.
>
> Main motivation is that fault handler doesn't need to be aware of
> readahead algorithms but just should call swapin_readahead.
>
> As first step, this patch cleans up a little bit but not perfect
> (I just separate for review easier) so next patch will make the goal
> complete.
>
> Signed-off-by: Minchan Kim <minchan@...nel.org>
> ---
> include/linux/swap.h | 17 ++--------
> mm/memory.c | 17 +++-------
> mm/swap_state.c | 89 ++++++++++++++++++++++++++++------------------------
> 3 files changed, 55 insertions(+), 68 deletions(-)
>
> diff --git a/include/linux/swap.h b/include/linux/swap.h
> index 84255b3da7c1..7c7c8b344bc9 100644
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -427,12 +427,8 @@ extern struct page *__read_swap_cache_async(swp_entry_t, gfp_t,
> bool *new_page_allocated);
> extern struct page *swapin_readahead(swp_entry_t, gfp_t,
> struct vm_area_struct *vma, unsigned long addr);
> -
> -extern struct page *swap_readahead_detect(struct vm_fault *vmf,
> - struct vma_swap_readahead *swap_ra);
> extern struct page *do_swap_page_readahead(swp_entry_t fentry, gfp_t gfp_mask,
> - struct vm_fault *vmf,
> - struct vma_swap_readahead *swap_ra);
> + struct vm_fault *vmf);
>
> /* linux/mm/swapfile.c */
> extern atomic_long_t nr_swap_pages;
> @@ -551,15 +547,8 @@ static inline bool swap_use_vma_readahead(void)
> return false;
> }
>
> -static inline struct page *swap_readahead_detect(
> - struct vm_fault *vmf, struct vma_swap_readahead *swap_ra)
> -{
> - return NULL;
> -}
> -
> -static inline struct page *do_swap_page_readahead(
> - swp_entry_t fentry, gfp_t gfp_mask,
> - struct vm_fault *vmf, struct vma_swap_readahead *swap_ra)
> +static inline struct page *do_swap_page_readahead(swp_entry_t fentry,
> + gfp_t gfp_mask, struct vm_fault *vmf)
> {
> return NULL;
> }
> diff --git a/mm/memory.c b/mm/memory.c
> index 8a0c410037d2..e955298e4290 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2849,21 +2849,14 @@ int do_swap_page(struct vm_fault *vmf)
> struct vm_area_struct *vma = vmf->vma;
> struct page *page = NULL, *swapcache = NULL;
> struct mem_cgroup *memcg;
> - struct vma_swap_readahead swap_ra;
> swp_entry_t entry;
> pte_t pte;
> int locked;
> int exclusive = 0;
> int ret = 0;
> - bool vma_readahead = swap_use_vma_readahead();
>
> - if (vma_readahead)
> - page = swap_readahead_detect(vmf, &swap_ra);
> - if (!pte_unmap_same(vma->vm_mm, vmf->pmd, vmf->pte, vmf->orig_pte)) {
> - if (page)
> - put_page(page);
> + if (!pte_unmap_same(vma->vm_mm, vmf->pmd, vmf->pte, vmf->orig_pte))
> goto out;
> - }
The page table holding PTE may be unmapped in pte_unmap_same(), so is it
safe for us to access page table after this in do_swap_page_readahead()?
Best Regards,
Huang, Ying
> entry = pte_to_swp_entry(vmf->orig_pte);
> if (unlikely(non_swap_entry(entry))) {
> @@ -2889,9 +2882,7 @@ int do_swap_page(struct vm_fault *vmf)
>
>
> delayacct_set_flag(DELAYACCT_PF_SWAPIN);
> - if (!page)
> - page = lookup_swap_cache(entry, vma_readahead ? vma : NULL,
> - vmf->address);
> + page = lookup_swap_cache(entry, vma, vmf->address);
> if (!page) {
> struct swap_info_struct *si = swp_swap_info(entry);
>
> @@ -2907,9 +2898,9 @@ int do_swap_page(struct vm_fault *vmf)
> swap_readpage(page, true);
> }
> } else {
> - if (vma_readahead)
> + if (swap_use_vma_readahead())
> page = do_swap_page_readahead(entry,
> - GFP_HIGHUSER_MOVABLE, vmf, &swap_ra);
> + GFP_HIGHUSER_MOVABLE, vmf);
> else
> page = swapin_readahead(entry,
> GFP_HIGHUSER_MOVABLE, vma, vmf->address);
> diff --git a/mm/swap_state.c b/mm/swap_state.c
> index 6c017ced11e6..e3c535fcd2df 100644
> --- a/mm/swap_state.c
> +++ b/mm/swap_state.c
> @@ -331,32 +331,38 @@ struct page *lookup_swap_cache(swp_entry_t entry, struct vm_area_struct *vma,
> unsigned long addr)
> {
> struct page *page;
> - unsigned long ra_info;
> - int win, hits, readahead;
>
> page = find_get_page(swap_address_space(entry), swp_offset(entry));
>
> INC_CACHE_INFO(find_total);
> if (page) {
> + bool vma_ra = swap_use_vma_readahead();
> + bool readahead = TestClearPageReadahead(page);
> +
> INC_CACHE_INFO(find_success);
> if (unlikely(PageTransCompound(page)))
> return page;
> - readahead = TestClearPageReadahead(page);
> - if (vma) {
> - ra_info = GET_SWAP_RA_VAL(vma);
> - win = SWAP_RA_WIN(ra_info);
> - hits = SWAP_RA_HITS(ra_info);
> +
> + if (vma && vma_ra) {
> + unsigned long ra_val;
> + int win, hits;
> +
> + ra_val = GET_SWAP_RA_VAL(vma);
> + win = SWAP_RA_WIN(ra_val);
> + hits = SWAP_RA_HITS(ra_val);
> if (readahead)
> hits = min_t(int, hits + 1, SWAP_RA_HITS_MAX);
> atomic_long_set(&vma->swap_readahead_info,
> SWAP_RA_VAL(addr, win, hits));
> }
> +
> if (readahead) {
> count_vm_event(SWAP_RA_HIT);
> - if (!vma)
> + if (!vma || !vma_ra)
> atomic_inc(&swapin_readahead_hits);
> }
> }
> +
> return page;
> }
>
> @@ -645,16 +651,15 @@ static inline void swap_ra_clamp_pfn(struct vm_area_struct *vma,
> PFN_DOWN((faddr & PMD_MASK) + PMD_SIZE));
> }
>
> -struct page *swap_readahead_detect(struct vm_fault *vmf,
> - struct vma_swap_readahead *swap_ra)
> +static void swap_ra_info(struct vm_fault *vmf,
> + struct vma_swap_readahead *ra_info)
> {
> struct vm_area_struct *vma = vmf->vma;
> - unsigned long swap_ra_info;
> - struct page *page;
> + unsigned long ra_val;
> swp_entry_t entry;
> unsigned long faddr, pfn, fpfn;
> unsigned long start, end;
> - pte_t *pte;
> + pte_t *pte, *orig_pte;
> unsigned int max_win, hits, prev_win, win, left;
> #ifndef CONFIG_64BIT
> pte_t *tpte;
> @@ -663,30 +668,32 @@ struct page *swap_readahead_detect(struct vm_fault *vmf,
> max_win = 1 << min_t(unsigned int, READ_ONCE(page_cluster),
> SWAP_RA_ORDER_CEILING);
> if (max_win == 1) {
> - swap_ra->win = 1;
> - return NULL;
> + ra_info->win = 1;
> + return;
> }
>
> faddr = vmf->address;
> - entry = pte_to_swp_entry(vmf->orig_pte);
> - if ((unlikely(non_swap_entry(entry))))
> - return NULL;
> - page = lookup_swap_cache(entry, vma, faddr);
> - if (page)
> - return page;
> + orig_pte = pte = pte_offset_map(vmf->pmd, faddr);
> + entry = pte_to_swp_entry(*pte);
> + if ((unlikely(non_swap_entry(entry)))) {
> + pte_unmap(orig_pte);
> + return;
> + }
>
> fpfn = PFN_DOWN(faddr);
> - swap_ra_info = GET_SWAP_RA_VAL(vma);
> - pfn = PFN_DOWN(SWAP_RA_ADDR(swap_ra_info));
> - prev_win = SWAP_RA_WIN(swap_ra_info);
> - hits = SWAP_RA_HITS(swap_ra_info);
> - swap_ra->win = win = __swapin_nr_pages(pfn, fpfn, hits,
> + ra_val = GET_SWAP_RA_VAL(vma);
> + pfn = PFN_DOWN(SWAP_RA_ADDR(ra_val));
> + prev_win = SWAP_RA_WIN(ra_val);
> + hits = SWAP_RA_HITS(ra_val);
> + ra_info->win = win = __swapin_nr_pages(pfn, fpfn, hits,
> max_win, prev_win);
> atomic_long_set(&vma->swap_readahead_info,
> SWAP_RA_VAL(faddr, win, 0));
>
> - if (win == 1)
> - return NULL;
> + if (win == 1) {
> + pte_unmap(orig_pte);
> + return;
> + }
>
> /* Copy the PTEs because the page table may be unmapped */
> if (fpfn == pfn + 1)
> @@ -699,23 +706,21 @@ struct page *swap_readahead_detect(struct vm_fault *vmf,
> swap_ra_clamp_pfn(vma, faddr, fpfn - left, fpfn + win - left,
> &start, &end);
> }
> - swap_ra->nr_pte = end - start;
> - swap_ra->offset = fpfn - start;
> - pte = vmf->pte - swap_ra->offset;
> + ra_info->nr_pte = end - start;
> + ra_info->offset = fpfn - start;
> + pte -= ra_info->offset;
> #ifdef CONFIG_64BIT
> - swap_ra->ptes = pte;
> + ra_info->ptes = pte;
> #else
> - tpte = swap_ra->ptes;
> + tpte = ra_info->ptes;
> for (pfn = start; pfn != end; pfn++)
> *tpte++ = *pte++;
> #endif
> -
> - return NULL;
> + pte_unmap(orig_pte);
> }
>
> struct page *do_swap_page_readahead(swp_entry_t fentry, gfp_t gfp_mask,
> - struct vm_fault *vmf,
> - struct vma_swap_readahead *swap_ra)
> + struct vm_fault *vmf)
> {
> struct blk_plug plug;
> struct vm_area_struct *vma = vmf->vma;
> @@ -724,12 +729,14 @@ struct page *do_swap_page_readahead(swp_entry_t fentry, gfp_t gfp_mask,
> swp_entry_t entry;
> unsigned int i;
> bool page_allocated;
> + struct vma_swap_readahead ra_info = {0,};
>
> - if (swap_ra->win == 1)
> + swap_ra_info(vmf, &ra_info);
> + if (ra_info.win == 1)
> goto skip;
>
> blk_start_plug(&plug);
> - for (i = 0, pte = swap_ra->ptes; i < swap_ra->nr_pte;
> + for (i = 0, pte = ra_info.ptes; i < ra_info.nr_pte;
> i++, pte++) {
> pentry = *pte;
> if (pte_none(pentry))
> @@ -745,7 +752,7 @@ struct page *do_swap_page_readahead(swp_entry_t fentry, gfp_t gfp_mask,
> continue;
> if (page_allocated) {
> swap_readpage(page, false);
> - if (i != swap_ra->offset &&
> + if (i != ra_info.offset &&
> likely(!PageTransCompound(page))) {
> SetPageReadahead(page);
> count_vm_event(SWAP_RA);
> @@ -757,7 +764,7 @@ struct page *do_swap_page_readahead(swp_entry_t fentry, gfp_t gfp_mask,
> lru_add_drain();
> skip:
> return read_swap_cache_async(fentry, gfp_mask, vma, vmf->address,
> - swap_ra->win == 1);
> + ra_info.win == 1);
> }
>
> #ifdef CONFIG_SYSFS
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