On Fri, Dec 29, 2017 at 09:00:16AM +0900, Minchan Kim wrote: > On Thu, Dec 28, 2017 at 11:00:40AM -0800, James Bottomley wrote: > > On Thu, 2017-12-28 at 09:41 -0800, James Bottomley wrote: > > > I'd guess that since they're both in io_schedule, the problem is that > > > the io_scheduler is taking far too long servicing the requests due to > > > some priority issue you've introduced. > > > > OK, so after some analysis, that turned out to be incorrect. The > > problem seems to be that we're exiting do_swap_page() with locked pages > > that have been read in from swap. > > > > Your changelogs are entirely unclear on why you changed the swapcache > > setting logic in this patch: > > > > commit 0bcac06f27d7528591c27ac2b093ccd71c5d0168 > > Author: Minchan Kim <minchan@xxxxxxxxxx> > > Date: Wed Nov 15 17:33:07 2017 -0800 > > > > mm, swap: skip swapcache for swapin of synchronous device > > > > But I think you're using swapcache == NULL as a signal the page came > > from a synchronous device. In which case the bug is that you've > > Exactly. Because the patchset aims for skipping swap cache for synchronous > device and some logics of do_swap_page has has assumed the page is on > swap cache. > > > forgotten we may already have picked up a page in > > swap_readahead_detect() which you're wrongly keeping swapcache == NULL > > for and the fix is this (it works on my system, although I'm still > > getting an unaccountable shutdown delay). > > SIGH. I missed that. > > > > > I still think we should revert this series, because this may not be the > > only bug lurking in the code, so it should go through a lot more > > rigorous testing than it has. > > I have no problem. It's not urgent. > > Andrew, this is reverting patch based on 4.15-rc5. And I need to send > another revert patch against on mmotm because it would have conflict due to > vma-based readahead restructuring patch. I will send soon. > We should revert (23c47d2ada9f, bdi: introduce BDI_CAP_SYNCHRONOUS_IO) as well. I resend reverting patch with including 23c47d2ada9f. Andrew, Pleas take this patch for linus-tree. Sorry for the confusion. >From d2d4116a8ebfafd66efd2cd1ae9db6c8f6049ec0 Mon Sep 17 00:00:00 2001 From: Minchan Kim <minchan@xxxxxxxxxx> Date: Fri, 29 Dec 2017 08:09:06 +0900 Subject: [PATCH] mm: Revert skip swap cache feture for synchronous device James reported a bug of swap paging-in for his testing and found it at rc5, soon to be -rc5. Although we can fix the specific problem at the moment, it may have other lurkig bugs so want to have one more cycle in -next before merging. This patchset reverts 23c47d2ada9f, 08fa93021d80, 8e31f339295f completely but 79b5f08fa34e partially because the swp_swap_info function that 79b5f08fa34e introduced is used by [1]. [1] e9a6effa5005, mm, swap: fix false error message in __swp_swapcount() Link: http://lkml.kernel.org/r/<1514407817.4169.4.camel@xxxxxxxxxxxxxxxxxxxxx> Cc: Christoph Hellwig <hch@xxxxxx> Cc: Dan Williams <dan.j.williams@xxxxxxxxx> Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Ilya Dryomov <idryomov@xxxxxxxxx> Cc: Jens Axboe <axboe@xxxxxxxxx> Cc: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx> Cc: Huang Ying <ying.huang@xxxxxxxxx> Debugged-by: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx> --- drivers/block/brd.c | 2 -- drivers/block/zram/zram_drv.c | 2 +- drivers/nvdimm/btt.c | 3 --- drivers/nvdimm/pmem.c | 2 -- include/linux/backing-dev.h | 8 ------- include/linux/swap.h | 14 +----------- mm/memory.c | 53 +++++++++++++------------------------------ mm/page_io.c | 6 ++--- mm/swapfile.c | 12 ++-------- 9 files changed, 23 insertions(+), 79 deletions(-) diff --git a/drivers/block/brd.c b/drivers/block/brd.c index 8028a3a7e7fd..3d8e29ad0159 100644 --- a/drivers/block/brd.c +++ b/drivers/block/brd.c @@ -20,7 +20,6 @@ #include <linux/radix-tree.h> #include <linux/fs.h> #include <linux/slab.h> -#include <linux/backing-dev.h> #include <linux/uaccess.h> @@ -401,7 +400,6 @@ static struct brd_device *brd_alloc(int i) disk->flags = GENHD_FL_EXT_DEVT; sprintf(disk->disk_name, "ram%d", i); set_capacity(disk, rd_size * 2); - disk->queue->backing_dev_info->capabilities |= BDI_CAP_SYNCHRONOUS_IO; return brd; diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index d70eba30003a..36117f649e53 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -1558,7 +1558,7 @@ static int zram_add(void) blk_queue_max_write_zeroes_sectors(zram->disk->queue, UINT_MAX); zram->disk->queue->backing_dev_info->capabilities |= - (BDI_CAP_STABLE_WRITES | BDI_CAP_SYNCHRONOUS_IO); + BDI_CAP_STABLE_WRITES; add_disk(zram->disk); ret = sysfs_create_group(&disk_to_dev(zram->disk)->kobj, diff --git a/drivers/nvdimm/btt.c b/drivers/nvdimm/btt.c index c586bcdb5190..09428ebd315b 100644 --- a/drivers/nvdimm/btt.c +++ b/drivers/nvdimm/btt.c @@ -23,7 +23,6 @@ #include <linux/ndctl.h> #include <linux/fs.h> #include <linux/nd.h> -#include <linux/backing-dev.h> #include "btt.h" #include "nd.h" @@ -1536,8 +1535,6 @@ static int btt_blk_init(struct btt *btt) btt->btt_disk->private_data = btt; btt->btt_disk->queue = btt->btt_queue; btt->btt_disk->flags = GENHD_FL_EXT_DEVT; - btt->btt_disk->queue->backing_dev_info->capabilities |= - BDI_CAP_SYNCHRONOUS_IO; blk_queue_make_request(btt->btt_queue, btt_make_request); blk_queue_logical_block_size(btt->btt_queue, btt->sector_size); diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c index 7fbc5c5dc8e1..39dfd7affa31 100644 --- a/drivers/nvdimm/pmem.c +++ b/drivers/nvdimm/pmem.c @@ -31,7 +31,6 @@ #include <linux/uio.h> #include <linux/dax.h> #include <linux/nd.h> -#include <linux/backing-dev.h> #include "pmem.h" #include "pfn.h" #include "nd.h" @@ -395,7 +394,6 @@ static int pmem_attach_disk(struct device *dev, disk->fops = &pmem_fops; disk->queue = q; disk->flags = GENHD_FL_EXT_DEVT; - disk->queue->backing_dev_info->capabilities |= BDI_CAP_SYNCHRONOUS_IO; nvdimm_namespace_disk_name(ndns, disk->disk_name); set_capacity(disk, (pmem->size - pmem->pfn_pad - pmem->data_offset) / 512); diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h index e54e7e0033eb..6fe54fd1b70d 100644 --- a/include/linux/backing-dev.h +++ b/include/linux/backing-dev.h @@ -122,8 +122,6 @@ int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio); * BDI_CAP_STRICTLIMIT: Keep number of dirty pages below bdi threshold. * * BDI_CAP_CGROUP_WRITEBACK: Supports cgroup-aware writeback. - * BDI_CAP_SYNCHRONOUS_IO: Device is so fast that asynchronous IO would be - * inefficient. */ #define BDI_CAP_NO_ACCT_DIRTY 0x00000001 #define BDI_CAP_NO_WRITEBACK 0x00000002 @@ -131,7 +129,6 @@ int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio); #define BDI_CAP_STABLE_WRITES 0x00000008 #define BDI_CAP_STRICTLIMIT 0x00000010 #define BDI_CAP_CGROUP_WRITEBACK 0x00000020 -#define BDI_CAP_SYNCHRONOUS_IO 0x00000040 #define BDI_CAP_NO_ACCT_AND_WRITEBACK \ (BDI_CAP_NO_WRITEBACK | BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_ACCT_WB) @@ -177,11 +174,6 @@ static inline int wb_congested(struct bdi_writeback *wb, int cong_bits) long congestion_wait(int sync, long timeout); long wait_iff_congested(struct pglist_data *pgdat, int sync, long timeout); -static inline bool bdi_cap_synchronous_io(struct backing_dev_info *bdi) -{ - return bdi->capabilities & BDI_CAP_SYNCHRONOUS_IO; -} - static inline bool bdi_cap_stable_pages_required(struct backing_dev_info *bdi) { return bdi->capabilities & BDI_CAP_STABLE_WRITES; diff --git a/include/linux/swap.h b/include/linux/swap.h index c2b8128799c1..3799d8dbdad6 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -171,9 +171,8 @@ enum { SWP_AREA_DISCARD = (1 << 8), /* single-time swap area discards */ SWP_PAGE_DISCARD = (1 << 9), /* freed swap page-cluster discards */ SWP_STABLE_WRITES = (1 << 10), /* no overwrite PG_writeback pages */ - SWP_SYNCHRONOUS_IO = (1 << 11), /* synchronous IO is efficient */ /* add others here before... */ - SWP_SCANNING = (1 << 12), /* refcount in scan_swap_map */ + SWP_SCANNING = (1 << 11), /* refcount in scan_swap_map */ }; #define SWAP_CLUSTER_MAX 32UL @@ -474,7 +473,6 @@ 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 *); @@ -487,11 +485,6 @@ 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; @@ -601,11 +594,6 @@ static inline int page_swapcount(struct page *page) return 0; } -static inline int __swap_count(struct swap_info_struct *si, swp_entry_t entry) -{ - return 0; -} - static inline int __swp_swapcount(swp_entry_t entry) { return 0; diff --git a/mm/memory.c b/mm/memory.c index ca5674cbaff2..0910abaf74b4 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2847,7 +2847,7 @@ 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 = NULL; + struct page *page = NULL, *swapcache; struct mem_cgroup *memcg; struct vma_swap_readahead swap_ra; swp_entry_t entry; @@ -2886,36 +2886,17 @@ 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) { - struct swap_info_struct *si = swp_swap_info(entry); - - if (si->flags & SWP_SYNCHRONOUS_IO && - __swap_count(si, entry) == 1) { - /* 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); - } - } 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 (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); if (!page) { /* * Back out if somebody else faulted in this pte @@ -2944,6 +2925,7 @@ int do_swap_page(struct vm_fault *vmf) goto out_release; } + swapcache = page; locked = lock_page_or_retry(page, vma->vm_mm, vmf->flags); delayacct_clear_flag(DELAYACCT_PF_SWAPIN); @@ -2958,8 +2940,7 @@ int do_swap_page(struct vm_fault *vmf) * test below, are not enough to exclude that. Even if it is still * swapcache, we need to check that the page's swap has not changed. */ - if (unlikely((!PageSwapCache(page) || - page_private(page) != entry.val)) && swapcache) + if (unlikely(!PageSwapCache(page) || page_private(page) != entry.val)) goto out_page; page = ksm_might_need_to_copy(page, vma, vmf->address); @@ -3012,16 +2993,14 @@ int do_swap_page(struct vm_fault *vmf) pte = pte_mksoft_dirty(pte); set_pte_at(vma->vm_mm, vmf->address, vmf->pte, pte); vmf->orig_pte = pte; - - /* ksm created a completely new copy */ - if (unlikely(page != swapcache && swapcache)) { - page_add_new_anon_rmap(page, vma, vmf->address, false); - mem_cgroup_commit_charge(page, memcg, false, false); - lru_cache_add_active_or_unevictable(page, vma); - } else { + if (page == swapcache) { do_page_add_anon_rmap(page, vma, vmf->address, exclusive); mem_cgroup_commit_charge(page, memcg, true, false); activate_page(page); + } else { /* ksm created a completely new copy */ + page_add_new_anon_rmap(page, vma, vmf->address, false); + mem_cgroup_commit_charge(page, memcg, false, false); + lru_cache_add_active_or_unevictable(page, vma); } swap_free(entry); @@ -3029,7 +3008,7 @@ int do_swap_page(struct vm_fault *vmf) (vma->vm_flags & VM_LOCKED) || PageMlocked(page)) try_to_free_swap(page); unlock_page(page); - if (page != swapcache && swapcache) { + if (page != swapcache) { /* * Hold the lock to avoid the swap entry to be reused * until we take the PT lock for the pte_same() check @@ -3062,7 +3041,7 @@ int do_swap_page(struct vm_fault *vmf) unlock_page(page); out_release: put_page(page); - if (page != swapcache && swapcache) { + if (page != swapcache) { unlock_page(swapcache); put_page(swapcache); } diff --git a/mm/page_io.c b/mm/page_io.c index e93f1a4cacd7..cd52b9cc169b 100644 --- a/mm/page_io.c +++ b/mm/page_io.c @@ -347,7 +347,7 @@ int __swap_writepage(struct page *page, struct writeback_control *wbc, return ret; } -int swap_readpage(struct page *page, bool synchronous) +int swap_readpage(struct page *page, bool do_poll) { struct bio *bio; int ret = 0; @@ -355,7 +355,7 @@ int swap_readpage(struct page *page, bool synchronous) blk_qc_t qc; struct gendisk *disk; - VM_BUG_ON_PAGE(!PageSwapCache(page) && !synchronous, page); + VM_BUG_ON_PAGE(!PageSwapCache(page), page); VM_BUG_ON_PAGE(!PageLocked(page), page); VM_BUG_ON_PAGE(PageUptodate(page), page); if (frontswap_load(page) == 0) { @@ -403,7 +403,7 @@ int swap_readpage(struct page *page, bool synchronous) count_vm_event(PSWPIN); bio_get(bio); qc = submit_bio(bio); - while (synchronous) { + while (do_poll) { set_current_state(TASK_UNINTERRUPTIBLE); if (!READ_ONCE(bio->bi_private)) break; diff --git a/mm/swapfile.c b/mm/swapfile.c index 3074b02eaa09..08f610ca635c 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -1328,13 +1328,6 @@ int page_swapcount(struct page *page) return count; } -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]); -} - static int swap_swapcount(struct swap_info_struct *si, swp_entry_t entry) { int count = 0; @@ -3176,9 +3169,6 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags) if (bdi_cap_stable_pages_required(inode_to_bdi(inode))) p->flags |= SWP_STABLE_WRITES; - if (bdi_cap_synchronous_io(inode_to_bdi(inode))) - p->flags |= SWP_SYNCHRONOUS_IO; - if (p->bdev && blk_queue_nonrot(bdev_get_queue(p->bdev))) { int cpu; unsigned long ci, nr_cluster; @@ -3478,6 +3468,7 @@ struct swap_info_struct *page_swap_info(struct page *page) */ struct address_space *__page_file_mapping(struct page *page) { + VM_BUG_ON_PAGE(!PageSwapCache(page), page); return page_swap_info(page)->swap_file->f_mapping; } EXPORT_SYMBOL_GPL(__page_file_mapping); @@ -3485,6 +3476,7 @@ EXPORT_SYMBOL_GPL(__page_file_mapping); pgoff_t __page_file_index(struct page *page) { swp_entry_t swap = { .val = page_private(page) }; + VM_BUG_ON_PAGE(!PageSwapCache(page), page); return swp_offset(swap); } EXPORT_SYMBOL_GPL(__page_file_index); -- 2.7.4 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. 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