On Tue, Feb 9, 2021 at 12:21 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
>
> Yeah, I have trouble with the private2 vs fscache bit too. I've been
> trying to persuade David that he doesn't actually need an fscache
> bit at all; he can just increment the page's refcount to prevent it
> from being freed while he writes data to the cache.
Does the code not hold a refcount already?
Honestly, the fact that writeback doesn't take a refcount, and then
has magic "if writeback is set, don't free" code in other parts of the
VM layer has been a problem already, when the wakeup ended up
"leaking" from a previous page to a new allocation.
I very much hope the fscache bit does not make similar mistakes,
because the rest of the VM will _not_ have special "if fscache is set,
then we won't do X" the way we do for writeback.
So I think the fscache code needs to hold a refcount regardless, and
that the fscache bit is set the page has to have a reference.
So what are the current lifetime rules for the fscache bit?
Linus
