在 2022/4/15 14:44, Yu Zhao 写道:
On Fri, Apr 15, 2022 at 02:31:37PM +0800, Chen Wandun wrote:
在 2022/4/15 13:25, Yu Zhao 写道:
On Fri, Apr 15, 2022 at 10:23:18AM +0800, Chen Wandun wrote:
在 2022/4/15 4:53, Yu Zhao 写道:
On Thu, Apr 14, 2022 at 07:47:54PM +0800, Chen Wandun wrote:
On 2022/4/7 11:15, Yu Zhao wrote:
+static void inc_min_seq(struct lruvec *lruvec)
+{
+ int type;
+ struct lru_gen_struct *lrugen = &lruvec->lrugen;
+
+ VM_BUG_ON(!seq_is_valid(lruvec));
+
+ for (type = 0; type < ANON_AND_FILE; type++) {
+ if (get_nr_gens(lruvec, type) != MAX_NR_GENS)
+ continue;
I'm confused about relation between aging and LRU list operation.
In function inc_max_seq, both min_seq and max_seq will increase，
the lrugen->lists[] indexed by lru_gen_from_seq(max_seq + 1) may
be non-empty?
Yes.
for example,
before inc_max_seq:
min_seq == 0, lrugen->lists[0][type][zone]
max_seq ==3, lrugen->lists[3][type][zone]
after inc_max_seq:
min_seq ==1, lrugen->lists[1][type][zone]
max_seq ==4, lrugen->lists[0][type][zone]
If lrugen->lists[0][type][zone] is not empty before inc_max_seq and it is
the most inactive list，however lurgen->lists[0][type][zone] will become
the most active list after inc_max_seq.
Correct.
So, in this place,
if (get_nr_gens(lruvec, type) != MAX_NR_GENS)
continue;
should change to
if (get_nr_gens(lruvec, type) == MAX_NR_GENS)
continue;
No, because max/min_seq will overlap if we do so.
lrugen->lists[max_seq+1] can only be non-empty for anon LRU, for a
couple of reasons:
1. We can't swap at all.
2. Swapping is constrained, e.g., swapfile is full.
Both cases are similar to a producer (the aging) overrunning a
consumer (the eviction). We used to handle them, but I simplified the
code because I don't feel they are worth handling [1].
Can lrugen->lists[max_seq+1] also be non-empty for file LRU？
On reclaim path, no. But it can be forced to do so via debugfs.
such as in dont reclaim mapped file page case(isolation will fail).
You mean may_unmap=false? Pages stays in the same generation if
isolation fails. So lrugen->lists[min_seq] won't be empty in this
case.
If so, after aging, eviction will reclaim memory start from
lrugen->lists[min_seq+1], but some oldest file page still
remain in lrugen->lists[max_seq+1].
sort_folio can help to put misplaced pages to the right
LRU list, but in this case, it does't help, because sort_folio
only sort lrugen->lists[min_seq+1].
On reclaim path, inc_max_seq() is only called when need_aging=true,
and this guarantees max_seq-min_seq[LRU_GEN_FILE]+1 < MAX_NR_GENS.
yes, I think so, but I did't find the logical in function get_nr_evictable,
or am I missing something
if (min_seq[LRU_GEN_FILE] + MIN_NR_GENS > max_seq)
*need_aging = true;
else if (min_seq[LRU_GEN_FILE] + MIN_NR_GENS < max_seq)
*need_aging = false;
This branch.
And the following is also relavent:
static int __init init_lru_gen(void)
{
BUILD_BUG_ON(MIN_NR_GENS + 1 >= MAX_NR_GENS);
Got it, many thanks.
Wandun
.
