Hi,In the system with very few file pages (nr_active_file + nr_inactive_file < 100), it is easy to reproduce "nr_isolated_file > nr_inactive_file", then too_many_isolated return true, shrink_inactive_list enter "msleep(100)", the long latency will happen.
The test case to reproduce it is very simple: allocate many huge pages(near the DRAM size), then do free, repeat the same operation many times. In the test case, the system with very few file pages (nr_active_file + nr_inactive_file < 100), I have dumpped the numbers of active/inactive/isolated file pages during the whole test(see in the attachments) , in shrink_inactive_list "too_many_isolated" is very easy to return true, then enter "msleep(100)",in "too_many_isolated" sc->gfp_mask is 0x342cca ("_GFP_IO" and "__GFP_FS" is masked) , it is also very easy to enter “inactive >>=3”, then “isolated > inactive” will be true.
So I have a proposal to set a threshold number for the total file pages to ignore the system with very few file pages, and then bypass the 100ms sleep. It is hard to set a perfect number for the threshold, so I just give an example of "256" for it.
I appreciate it if you can give me your suggestion/comments. Thanks. On 4/16/2021 10:35 AM, zhengjun.xing@xxxxxxxxxxxxxxx wrote:
From: Zhengjun Xing <zhengjun.xing@xxxxxxxxxxxxxxx> In the system with very few file pages, it is easy to reproduce "nr_isolated_file > nr_inactive_file", then too_many_isolated return true, shrink_inactive_list enter "msleep(100)", the long latency will happen. The test case to reproduce it is very simple, allocate a lot of huge pages (near the DRAM size), then do free, repeat the same operation many times. There is a 3/10 rate to reproduce the issue. In the test, sc-> gfp_mask is 0x342cca ("_GFP_IO" and "__GFP_FS" is masked),it is more easy to enter “inactive >>=3”, then “isolated > inactive” will easy to be true. So I have a proposal to set a threshold number for the total file pages to ignore the system with very few file pages, and then bypass the 100ms sleep. It is hard to set a perfect number for the threshold, so I just give an example of "256" for it, need more inputs for it. Signed-off-by: Zhengjun Xing <zhengjun.xing@xxxxxxxxxxxxxxx> --- mm/vmscan.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 562e87cbd7a1..a1926463455c 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -168,6 +168,7 @@ struct scan_control { * From 0 .. 200. Higher means more swappy. */ int vm_swappiness = 60; +int lru_list_threshold = SWAP_CLUSTER_MAX << 3;static void set_task_reclaim_state(struct task_struct *task,struct reclaim_state *rs) @@ -1785,7 +1786,7 @@ int isolate_lru_page(struct page *page) static int too_many_isolated(struct pglist_data *pgdat, int file, struct scan_control *sc) { - unsigned long inactive, isolated; + unsigned long inactive, isolated, active, nr_lru_pages;if (current_is_kswapd())return 0; @@ -1796,11 +1797,13 @@ static int too_many_isolated(struct pglist_data *pgdat, int file, if (file) { inactive = node_page_state(pgdat, NR_INACTIVE_FILE); isolated = node_page_state(pgdat, NR_ISOLATED_FILE); + active = node_page_state(pgdat, NR_ACTIVE_FILE); } else { inactive = node_page_state(pgdat, NR_INACTIVE_ANON); isolated = node_page_state(pgdat, NR_ISOLATED_ANON); + active = node_page_state(pgdat, NR_ACTIVE_ANON); } - + nr_lru_pages = inactive + active; /* * GFP_NOIO/GFP_NOFS callers are allowed to isolate more pages, so they * won't get blocked by normal direct-reclaimers, forming a circular @@ -1809,6 +1812,10 @@ static int too_many_isolated(struct pglist_data *pgdat, int file, if ((sc->gfp_mask & (__GFP_IO | __GFP_FS)) == (__GFP_IO | __GFP_FS)) inactive >>= 3;+ if (isolated > inactive)+ if (nr_lru_pages < lru_list_threshold) + return 0; + return isolated > inactive; }
-- Zhengjun Xing
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