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.
Thanks.
>From ba8b1b940777de674b579f6421ed9e89cfdb5581 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 tree
before merging.
This patchset reverts 08fa93021d80, 8e31f339295f completely but
79b5f08fa34e partially because the swp_swap_info function that
introduced by 79b5f08fa34e is used by [1].
[1] e9a6effa5005, mm, swap: fix false error message in __swp_swapcount()
Debugged-by: James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
---
include/linux/swap.h | 14 +-------------
mm/memory.c | 53 ++++++++++++++++------------------------------------
mm/page_io.c | 6 +++---
mm/swapfile.c | 12 ++----------
4 files changed, 22 insertions(+), 63 deletions(-)
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
--
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