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author | Hugh Dickins <hughd@google.com> | 2023-06-08 18:52:17 -0700 |
---|---|---|
committer | Andrew Morton <akpm@linux-foundation.org> | 2023-06-19 16:19:19 -0700 |
commit | 4f8fcf4ced0b7184149045818dcc2f9e2689b775 (patch) | |
tree | cd052e27e9c7a4b08d6743f463ad9bd121ec0ea3 /mm | |
parent | feda5c393a6c843c7bf1fc49e1381e2d3822b564 (diff) | |
download | lwn-4f8fcf4ced0b7184149045818dcc2f9e2689b775.tar.gz lwn-4f8fcf4ced0b7184149045818dcc2f9e2689b775.zip |
mm/swap: swap_vma_readahead() do the pte_offset_map()
swap_vma_readahead() has been proceeding in an unconventional way, its
preliminary swap_ra_info() doing the pte_offset_map() and pte_unmap(),
then relying on that pte pointer even after the pte_unmap() - in its
CONFIG_64BIT case (I think !CONFIG_HIGHPTE was intended; whereas 32-bit
copied ptes to stack while they were mapped, but had to limit how many).
Though it would be difficult to construct a failing testcase, accessing
page table after pte_unmap() will become bad practice, even on 64-bit: an
rcu_read_unlock() in pte_unmap() will allow page table to be freed.
Move relevant definitions from include/linux/swap.h to mm/swap_state.c,
nothing else used them. Delete the CONFIG_64BIT distinction and buffer,
delete all reference to ptes from swap_ra_info(), use pte_offset_map()
repeatedly in swap_vma_readahead(), breaking from the loop if it fails.
(Will the repeated "map" and "unmap" show up as a slowdown anywhere? If
so, maybe modify __read_swap_cache_async() to do the pte_unmap() only when
it does not find the page already in the swapcache.)
Use ptep_get_lockless(), mainly for its READ_ONCE(). Correctly advance
the address passed down to each call of __read__swap_cache_async().
Link: https://lkml.kernel.org/r/b7c64ab3-9e44-aac0-d2b-c57de578af1c@google.com
Signed-off-by: Hugh Dickins <hughd@google.com>
Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Song Liu <song@kernel.org>
Cc: Steven Price <steven.price@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Will Deacon <will@kernel.org>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Zack Rusin <zackr@vmware.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r-- | mm/swap_state.c | 45 |
1 files changed, 24 insertions, 21 deletions
diff --git a/mm/swap_state.c b/mm/swap_state.c index ef32353c18a6..a33c60e0158f 100644 --- a/mm/swap_state.c +++ b/mm/swap_state.c @@ -709,6 +709,14 @@ void exit_swap_address_space(unsigned int type) swapper_spaces[type] = NULL; } +#define SWAP_RA_ORDER_CEILING 5 + +struct vma_swap_readahead { + unsigned short win; + unsigned short offset; + unsigned short nr_pte; +}; + static void swap_ra_info(struct vm_fault *vmf, struct vma_swap_readahead *ra_info) { @@ -716,11 +724,7 @@ static void swap_ra_info(struct vm_fault *vmf, unsigned long ra_val; unsigned long faddr, pfn, fpfn, lpfn, rpfn; unsigned long start, end; - pte_t *pte, *orig_pte; unsigned int max_win, hits, prev_win, win; -#ifndef CONFIG_64BIT - pte_t *tpte; -#endif max_win = 1 << min_t(unsigned int, READ_ONCE(page_cluster), SWAP_RA_ORDER_CEILING); @@ -739,12 +743,9 @@ static void swap_ra_info(struct vm_fault *vmf, max_win, prev_win); atomic_long_set(&vma->swap_readahead_info, SWAP_RA_VAL(faddr, win, 0)); - if (win == 1) return; - /* Copy the PTEs because the page table may be unmapped */ - orig_pte = pte = pte_offset_map(vmf->pmd, faddr); if (fpfn == pfn + 1) { lpfn = fpfn; rpfn = fpfn + win; @@ -764,15 +765,6 @@ static void swap_ra_info(struct vm_fault *vmf, ra_info->nr_pte = end - start; ra_info->offset = fpfn - start; - pte -= ra_info->offset; -#ifdef CONFIG_64BIT - ra_info->ptes = pte; -#else - tpte = ra_info->ptes; - for (pfn = start; pfn != end; pfn++) - *tpte++ = *pte++; -#endif - pte_unmap(orig_pte); } /** @@ -796,7 +788,8 @@ static struct page *swap_vma_readahead(swp_entry_t fentry, gfp_t gfp_mask, struct swap_iocb *splug = NULL; struct vm_area_struct *vma = vmf->vma; struct page *page; - pte_t *pte, pentry; + pte_t *pte = NULL, pentry; + unsigned long addr; swp_entry_t entry; unsigned int i; bool page_allocated; @@ -808,17 +801,25 @@ static struct page *swap_vma_readahead(swp_entry_t fentry, gfp_t gfp_mask, if (ra_info.win == 1) goto skip; + addr = vmf->address - (ra_info.offset * PAGE_SIZE); + blk_start_plug(&plug); - for (i = 0, pte = ra_info.ptes; i < ra_info.nr_pte; - i++, pte++) { - pentry = *pte; + for (i = 0; i < ra_info.nr_pte; i++, addr += PAGE_SIZE) { + if (!pte++) { + pte = pte_offset_map(vmf->pmd, addr); + if (!pte) + break; + } + pentry = ptep_get_lockless(pte); if (!is_swap_pte(pentry)) continue; entry = pte_to_swp_entry(pentry); if (unlikely(non_swap_entry(entry))) continue; + pte_unmap(pte); + pte = NULL; page = __read_swap_cache_async(entry, gfp_mask, vma, - vmf->address, &page_allocated); + addr, &page_allocated); if (!page) continue; if (page_allocated) { @@ -830,6 +831,8 @@ static struct page *swap_vma_readahead(swp_entry_t fentry, gfp_t gfp_mask, } put_page(page); } + if (pte) + pte_unmap(pte); blk_finish_plug(&plug); swap_read_unplug(splug); lru_add_drain(); |