On (24/02/27 03:02), Chengming Zhou wrote:
> Hello,
>
> free_zspage() has to hold locks of all pages, since zs_page_migrate()
> path rely on this page lock to protect the race between zs_free() and
> it, so it can safely get zspage from page->private.
>
> But this way is not good and simple enough:
>
> 1. Since zs_free() couldn't be sleepable, it can only trylock pages,
> or has to kick_deferred_free() to defer that to a work.
>
> 2. Even in the worker context, async_free_zspage() can't simply
> lock all pages in lock_zspage(), it's still trylock because of
> the race between zs_free() and zs_page_migrate(). Please see
> the commit 2505a981114d ("zsmalloc: fix races between asynchronous
> zspage free and page migration") for details.
>
> Actually, all free_zspage() needs is to get zspage from page safely,
> we can use RCU to achieve it easily. Then free_zspage() don't need to
> hold locks of all pages, so don't need the deferred free mechanism
> at all. This patchset implements it and remove all of deferred free
> related code.
>
> Thanks for review and comments!
>
> Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
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