Hi Hillf,
On 4/22/2021 6:23 PM, Hillf Danton wrote:
Hi Zhengjun
On Thu, 22 Apr 2021 16:36:19 +0800 Zhengjun Xing wrote:
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.
We should skip reclaiming page cache in this case.
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.
Another option seems like we take a nap at the second time of lru tmi
with some allocators in your case served without the 100ms delay.
+++ x/mm/vmscan.c
@@ -118,6 +118,9 @@ struct scan_control {
/* The file pages on the current node are dangerously low */
unsigned int file_is_tiny:1;
+ unsigned int file_tmi:1; /* too many isolated */
+ unsigned int anon_tmi:1;
+
/* Allocation order */
s8 order;
@@ -1905,6 +1908,21 @@ static int current_may_throttle(void)
bdi_write_congested(current->backing_dev_info);
}
+static void update_sc_tmi(struct scan_control *sc, bool file, int set)
+{
+ if (file)
+ sc->file_tmi = set;
+ else
+ sc->anon_tmi = set;
+}
+static bool is_sc_tmi(struct scan_control *sc, bool file)
+{
+ if (file)
+ return sc->file_tmi != 0;
+ else
+ return sc->anon_tmi != 0;
+}
+
/*
* shrink_inactive_list() is a helper for shrink_node(). It returns the number
* of reclaimed pages
@@ -1927,6 +1945,11 @@ shrink_inactive_list(unsigned long nr_to
if (stalled)
return 0;
+ if (!is_sc_tmi(sc, file)) {
+ update_sc_tmi(sc, file, 1);
+ return 0;
+ }
+
/* wait a bit for the reclaimer. */
msleep(100);
stalled = true;
@@ -1936,6 +1959,9 @@ shrink_inactive_list(unsigned long nr_to
return SWAP_CLUSTER_MAX;
}
+ if (is_sc_tmi(sc, file))
+ update_sc_tmi(sc, file, 0);
+
lru_add_drain();
spin_lock_irq(&lruvec->lru_lock);
I use my compaction test case to test it, 1/10 ratio can reproduce 100ms
sleep.
60) @ 103942.6 us | shrink_node();
60) @ 103795.8 us | shrink_node();
--
Zhengjun Xing
