+ z3fold-simplify-freeing-slots.patch added to -mm tree

+ z3fold-simplify-freeing-slots.patch added to -mm tree

[akpm]

The patch titled
     Subject: z3fold: simplify freeing slots
has been added to the -mm tree.  Its filename is
     z3fold-simplify-freeing-slots.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/z3fold-simplify-freeing-slots.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/z3fold-simplify-freeing-slots.patch

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next and is updated
there every 3-4 working days

------------------------------------------------------
From: Vitaly Wool <vitaly.wool@konsulko.com>
Subject: z3fold: simplify freeing slots

Patch series "z3fold: stability / rt fixes".

Address z3fold stability issues under stress load, primarily in the
reclaim and free aspects.  Besides, it fixes the locking problems that
were only seen in real-time kernel configuration.


This patch (of 3):

There used to be two places in the code where slots could be freed, namely
when freeing the last allocated handle from the slots and when releasing
the z3fold header these slots aree linked to.  The logic to decide on
whether to free certain slots was complicated and error prone in both
functions and it led to failures in RT case.

To fix that, make free_handle() the single point of freeing slots.

Link: https://lkml.kernel.org/r/20201209145151.18994-1-vitaly.wool@konsulko.com
Link: https://lkml.kernel.org/r/20201209145151.18994-2-vitaly.wool@konsulko.com
Signed-off-by: Vitaly Wool <vitaly.wool@konsulko.com>
Tested-by: Mike Galbraith <efault@gmx.de>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/z3fold.c |   55 +++++++++++---------------------------------------
 1 file changed, 13 insertions(+), 42 deletions(-)

--- a/mm/z3fold.c~z3fold-simplify-freeing-slots
+++ a/mm/z3fold.c
@@ -90,7 +90,7 @@ struct z3fold_buddy_slots {
 	 * be enough slots to hold all possible variants
 	 */
 	unsigned long slot[BUDDY_MASK + 1];
-	unsigned long pool; /* back link + flags */
+	unsigned long pool; /* back link */
 	rwlock_t lock;
 };
 #define HANDLE_FLAG_MASK	(0x03)
@@ -182,13 +182,6 @@ enum z3fold_page_flags {
 };
 
 /*
- * handle flags, go under HANDLE_FLAG_MASK
- */
-enum z3fold_handle_flags {
-	HANDLES_ORPHANED = 0,
-};
-
-/*
  * Forward declarations
  */
 static struct z3fold_header *__z3fold_alloc(struct z3fold_pool *, size_t, bool);
@@ -303,10 +296,9 @@ static inline void put_z3fold_header(str
 		z3fold_page_unlock(zhdr);
 }
 
-static inline void free_handle(unsigned long handle)
+static inline void free_handle(unsigned long handle, struct z3fold_header *zhdr)
 {
 	struct z3fold_buddy_slots *slots;
-	struct z3fold_header *zhdr;
 	int i;
 	bool is_free;
 
@@ -316,22 +308,13 @@ static inline void free_handle(unsigned
 	if (WARN_ON(*(unsigned long *)handle == 0))
 		return;
 
-	zhdr = handle_to_z3fold_header(handle);
 	slots = handle_to_slots(handle);
 	write_lock(&slots->lock);
 	*(unsigned long *)handle = 0;
-	if (zhdr->slots == slots) {
-		write_unlock(&slots->lock);
-		return; /* simple case, nothing else to do */
-	}
+	if (zhdr->slots != slots)
+		zhdr->foreign_handles--;
 
-	/* we are freeing a foreign handle if we are here */
-	zhdr->foreign_handles--;
 	is_free = true;
-	if (!test_bit(HANDLES_ORPHANED, &slots->pool)) {
-		write_unlock(&slots->lock);
-		return;
-	}
 	for (i = 0; i <= BUDDY_MASK; i++) {
 		if (slots->slot[i]) {
 			is_free = false;
@@ -343,6 +326,8 @@ static inline void free_handle(unsigned
 	if (is_free) {
 		struct z3fold_pool *pool = slots_to_pool(slots);
 
+		if (zhdr->slots == slots)
+			zhdr->slots = NULL;
 		kmem_cache_free(pool->c_handle, slots);
 	}
 }
@@ -525,8 +510,6 @@ static void __release_z3fold_page(struct
 {
 	struct page *page = virt_to_page(zhdr);
 	struct z3fold_pool *pool = zhdr_to_pool(zhdr);
-	bool is_free = true;
-	int i;
 
 	WARN_ON(!list_empty(&zhdr->buddy));
 	set_bit(PAGE_STALE, &page->private);
@@ -536,21 +519,6 @@ static void __release_z3fold_page(struct
 		list_del_init(&page->lru);
 	spin_unlock(&pool->lock);
 
-	/* If there are no foreign handles, free the handles array */
-	read_lock(&zhdr->slots->lock);
-	for (i = 0; i <= BUDDY_MASK; i++) {
-		if (zhdr->slots->slot[i]) {
-			is_free = false;
-			break;
-		}
-	}
-	if (!is_free)
-		set_bit(HANDLES_ORPHANED, &zhdr->slots->pool);
-	read_unlock(&zhdr->slots->lock);
-
-	if (is_free)
-		kmem_cache_free(pool->c_handle, zhdr->slots);
-
 	if (locked)
 		z3fold_page_unlock(zhdr);
 
@@ -973,6 +941,9 @@ lookup:
 		}
 	}
 
+	if (zhdr && !zhdr->slots)
+		zhdr->slots = alloc_slots(pool,
+					can_sleep ? GFP_NOIO : GFP_ATOMIC);
 	return zhdr;
 }
 
@@ -1270,7 +1241,7 @@ static void z3fold_free(struct z3fold_po
 	}
 
 	if (!page_claimed)
-		free_handle(handle);
+		free_handle(handle, zhdr);
 	if (kref_put(&zhdr->refcount, release_z3fold_page_locked_list)) {
 		atomic64_dec(&pool->pages_nr);
 		return;
@@ -1429,19 +1400,19 @@ static int z3fold_reclaim_page(struct z3
 			ret = pool->ops->evict(pool, middle_handle);
 			if (ret)
 				goto next;
-			free_handle(middle_handle);
+			free_handle(middle_handle, zhdr);
 		}
 		if (first_handle) {
 			ret = pool->ops->evict(pool, first_handle);
 			if (ret)
 				goto next;
-			free_handle(first_handle);
+			free_handle(first_handle, zhdr);
 		}
 		if (last_handle) {
 			ret = pool->ops->evict(pool, last_handle);
 			if (ret)
 				goto next;
-			free_handle(last_handle);
+			free_handle(last_handle, zhdr);
 		}
 next:
 		if (test_bit(PAGE_HEADLESS, &page->private)) {
_

Patches currently in -mm which might be from vitaly.wool@konsulko.com are

z3fold-simplify-freeing-slots.patch
z3fold-stricter-locking-and-more-careful-reclaim.patch
z3fold-remove-preempt-disabled-sections-for-rt.patch