On Thu, Feb 01, 2024 at 03:49:06PM +0000, Chengming Zhou wrote:
> Since we don't need to leave zswap entry on the zswap tree anymore,
> we should remove it from tree once we find it from the tree.
>
> Then after using it, we can directly free it, no concurrent path
> can find it from tree. Only the shrinker can see it from lru list,
> which will also double check under tree lock, so no race problem.
>
> So we don't need refcount in zswap entry anymore and don't need to
> take the spinlock for the second time to invalidate it.
>
> The side effect is that zswap_entry_free() maybe not happen in tree
> spinlock, but it's ok since nothing need to be protected by the lock.
>
> Signed-off-by: Chengming Zhou <[email protected]>
This looks like a great simplification, and a good motivation to only
support exclusive loads. Everything is more straightforward because
every tree lookup implies a removal and exclusive ownership.
Let's see if removing support for non-exclusive loads is agreeable first
though :)
On 2024/2/2 09:11, Yosry Ahmed wrote:
> On Thu, Feb 01, 2024 at 03:49:06PM +0000, Chengming Zhou wrote:
>> Since we don't need to leave zswap entry on the zswap tree anymore,
>> we should remove it from tree once we find it from the tree.
>>
>> Then after using it, we can directly free it, no concurrent path
>> can find it from tree. Only the shrinker can see it from lru list,
>> which will also double check under tree lock, so no race problem.
>>
>> So we don't need refcount in zswap entry anymore and don't need to
>> take the spinlock for the second time to invalidate it.
>>
>> The side effect is that zswap_entry_free() maybe not happen in tree
>> spinlock, but it's ok since nothing need to be protected by the lock.
>>
>> Signed-off-by: Chengming Zhou <[email protected]>
>
> This looks like a great simplification, and a good motivation to only
> support exclusive loads. Everything is more straightforward because
> every tree lookup implies a removal and exclusive ownership.
Right, much simpler!
>
> Let's see if removing support for non-exclusive loads is agreeable first
> though :)
Ok, I have just posted some testing data for discussion.
Thanks.