On 2020-07-09 01:32:38 [+0000], Song Bao Hua (Barry Song) wrote:
> > This looks using the same synchronous mechanism around an asynchronous
> > interface. It works as a PoC.
> >
> > As far as I remember the crypto async interface, the incoming skbs were fed to
> > the async interface and returned to the caller so the NIC could continue
> > allocate new RX skbs and move on. Only if the queue of requests was getting
> > to long the code started to throttle. Eventually the async crypto code
> > completed the decryption operation in a different context and fed the
> > decrypted packet(s) into the stack.
> >
> > From a quick view, you would have to return -EINPROGRESS here and have at
> > the caller side something like that:
> >
> > iff --git a/mm/page_io.c b/mm/page_io.c
> > index e8726f3e3820b..9d1baa46ec3ed 100644
> > --- a/mm/page_io.c
> > +++ b/mm/page_io.c
> > @@ -252,12 +252,15 @@ int swap_writepage(struct page *page, struct
> > writeback_control *wbc)
> > unlock_page(page);
> > goto out;
> > }
> > - if (frontswap_store(page) == 0) {
> > + ret = frontswap_store(page);
> > + if (ret == 0) {
> > set_page_writeback(page);
> > unlock_page(page);
> > end_page_writeback(page);
> > goto out;
> > }
> > + if (ret = -EINPROGRESS)
> > + goto out;
> > ret = __swap_writepage(page, wbc, end_swap_bio_write);
> > out:
> > return ret;
> >
> Unfortunately, this is not true and things are not that simple.
>
> We can't simply depend on -EINPROGRESS and go out.
> We have to wait for the result of compression to decide if we should
> do __swap_writepage(). As one page might be compressed into two
> pages, in this case, we will still need to do _swap_writepage().
> As I replied in the latest email, all of the async improvement to frontswap
> needs very careful thinking and benchmark. It can only happen after
> we build the base in this patch, fixing the broken connection between
> zswap and those new zip drivers.
At the time the compression finishes you see what happens and based on
the design you can either complete it immediately (the 0/error case from
above) or forward the result to the caller and let him decide.
> Thanks
> Barry
Sebastian
