On Sat, May 27, 2023 at 08:28:28PM +0100, Lorenzo Stoakes wrote:
> > static bool purge_fragmented_block(struct vmap_block *vb,
> > - struct vmap_block_queue *vbq, struct list_head *purge_list)
> > + struct vmap_block_queue *vbq, struct list_head *purge_list,
> > + bool force_purge)
> > {
> > if (vb->free + vb->dirty != VMAP_BBMAP_BITS ||
> > vb->dirty == VMAP_BBMAP_BITS)
> > return false;
> >
> > + /* Don't overeagerly purge usable blocks unless requested */
> > + if (!force_purge && vb->free < VMAP_PURGE_THRESHOLD)
>
> Little confused by this - if free capacity is less than the threshold, we
> _don't_ purge? I thought we should purge in this instance? Should this be an >=?
>
I'm pretty convinced this is incorrect, so here's a -fix patch to avoid
this staying in vmalloc by accident as Andrew has already taken it (using
De Morgan's law for clarity):-
----8<----
>From aa49ce7d5ca7937cfdf8f910e50296cf932f16cb Mon Sep 17 00:00:00 2001
From: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
Date: Mon, 5 Jun 2023 21:44:20 +0100
Subject: [PATCH] mm/vmalloc: Dont purge usable blocks unnecessarily
We do NOT purge if this conditional evalutates true, so correct
VMAP_PURGE_THRESHOLD check.
Signed-off-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
---
mm/vmalloc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index ab606a80f475..9d64a4098c36 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2102,7 +2102,7 @@ static bool purge_fragmented_block(struct vmap_block *vb,
return false;
/* Don't overeagerly purge usable blocks unless requested */
- if (!force_purge && vb->free < VMAP_PURGE_THRESHOLD)
+ if (!(force_purge || vb->free < VMAP_PURGE_THRESHOLD))
return false;
/* prevent further allocs after releasing lock */
--
2.40.
