z3fold: fix wrong handling of headless pages

During the processing of headless pages in z3fold_reclaim_page(), there was a problem that the zhdr pointed to another page or a page was already released in z3fold_free(). So, the wrong page is encoded in headless, or test_bit does not work properly in z3fold_reclaim_page(). This patch fixed these problems.

Signed-off-by Jongseok Kim <[email protected]>

---
 mm/z3fold.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

mm/z3fold.c +6 -3

index 4b366d1..201a8ac 100644
@@ -746,6 +746,9 @@ static void z3fold_free(struct z3fold_pool *pool, unsigned long handle)
        }
 
        if (bud == HEADLESS) {
+               if (test_bit(UNDER_RECLAIM, &page->private))
+                       return;
+
                spin_lock(&pool->lock);
                list_del(&page->lru);
                spin_unlock(&pool->lock);

@@ -836,20 +839,20 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
                }
                list_for_each_prev(pos, &pool->lru) {
                        page = list_entry(pos, struct page, lru);
+                       zhdr = page_address(page);
                        if (test_bit(PAGE_HEADLESS, &page->private))
                                /* candidate found */
                                break;
 
-                       zhdr = page_address(page);
                        if (!z3fold_page_trylock(zhdr))
                                continue; /* can't evict at this point */
                        kref_get(&zhdr->refcount);
                        list_del_init(&zhdr->buddy);
                        zhdr->cpu = -1;
-                       set_bit(UNDER_RECLAIM, &page->private);
                        break;
                }
 
+               set_bit(UNDER_RECLAIM, &page->private);
                list_del_init(&page->lru);
                spin_unlock(&pool->lock);
 

@@ -898,6 +901,7 @@ static int z3fold_reclaim_page(struct z3fold_pool *pool, unsigned int retries)
                if (test_bit(PAGE_HEADLESS, &page->private)) {
                        if (ret == 0) {
                                free_z3fold_page(page);
+                               atomic64_dec(&pool->pages_nr);
                                return 0;
                        }
                        spin_lock(&pool->lock);
--

2.7.4

2018년 11월 6일 (화) 오후 4:48, Vitaly Wool <[email protected]>님이 작성:
Hi Jongseok,

thank you for your work, we've now got a more comprehensive solution:
https://lkml.org/lkml/2018/11/5/726

Would you please confirm that it works for you? Also, would you be okay with dropping your patch in favor of the new one?

~Vitaly

Hi Jongseok,

thank you for your work, we've now got a more comprehensive solution:
https://lkml.org/lkml/2018/11/5/726

Would you please confirm that it works for you? Also, would you be okay with dropping your patch in favor of the new one?

~Vitaly

Hi Vitaly,
thank you for the reply.

I agree your a new solution is more comprehensive and drop my patch is simple way. But, I think it's not fair.
If my previous patch was not wrong, is (my patch -> your patch) the right way?

I'm sorry I sent reply twice.

Best regards,
Jongseok

Quoted 10 lines · Vitaly Wool

Hi Jongseok,

thank you for your work, we've now got a more comprehensive solution:
https://lkml.org/lkml/2018/11/5/726

Would you please confirm that it works for you? Also, would you be okay with dropping your patch in favor of the new one?

~Vitaly

Den tors 8 nov. 2018 kl 13:34 skrev +-eA 3/4 1/4 (R) <[email protected]>:

Quoted 7 lines

Hi Vitaly,
thank you for the reply.

I agree your a new solution is more comprehensive and drop my patch is simple way. But, I think it's not fair.
If my previous patch was not wrong, is (my patch -> your patch) the right way?

I could apply the new patch on top of yours but that would effectively revert most of your changes.
Would it be ok for you if I add you to Signed-off-by for the new patch instead?

~Vitaly

Quoted 16 lines

I'm sorry I sent reply twice.

Best regards,
Jongseok

Quoted 10 lines · Vitaly Wool

Hi Jongseok,

thank you for your work, we've now got a more comprehensive solution:
https://lkml.org/lkml/2018/11/5/726

Would you please confirm that it works for you? Also, would you be okay with dropping your patch in favor of the new one?

~Vitaly

Yes, you are right.
I think that's the best way to deal it.
Thank you.

Quoted 3 lines · On Thu, 8 Nov 2018 22:45:40 +0900 Jongseok Kim <[email protected]> wrote:

Yes, you are right.
I think that's the best way to deal it.
Thank you.

I did this:

Link:
http://lkml.kernel.org/r/[email protected]

Signed-off-by Vitaly Wool <[email protected]>

Signed-off-by Jongseok Kim <[email protected]>

Reported-by-by Jongseok Kim <[email protected]>

Reviewed-by Snild Dolkow <[email protected]>