Re: [PATCH] mm, zswap: don't touch the XArray lock if there is no entry to free

[Yosry Ahmed]

On Fri, Oct 18, 2024 at 1:55 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
>
> On Fri, Oct 18, 2024 at 01:40:18PM -0700, Yosry Ahmed wrote:
> > Oh I thought xas_reload() is enough here to check that the entry is
> > still there after the lock is acquired. Do we have to start the walk
> > over after holding the lock?
>
> Yes.  The entry is guaranteed to still be valid, but the node you're
> looking in might have been freed, so you can't modify the node without
> making sure the node is still in the tree.  We could make that cheaper
> than a rewalk, but you're going to need to write that code since you're
> the first to want to do something like this.

I see, thanks for elaborating.

Could you confirm if the current patch with the xas_reset() added
would be equivalent to just checking xa_load() before using
xa_erase()?