Re: [Qemu-devel] [PATCH v19 3/7] xbitmap: add more operations

[Tetsuo Handa]

Wei Wang wrote:
> > But passing GFP_NOWAIT means that we can handle allocation failure. There is
> > no need to use preload approach when we can handle allocation failure.
> 
> I think the reason we need xb_preload is because radix tree insertion 
> needs the memory being preallocated already (it couldn't suffer from 
> memory failure during the process of inserting, probably because 
> handling the failure there isn't easy, Matthew may know the backstory of 
> this)

According to https://lwn.net/Articles/175432/ , I think that preloading is 
needed
only when failure to insert an item into a radix tree is a significant problem.
That is, when failure to insert an item into a radix tree is not a problem,
I think that we don't need to use preloading.

> 
> So, I think we can handle the memory failure with xb_preload, which 
> stops going into the radix tree APIs, but shouldn't call radix tree APIs 
> without the related memory preallocated.

It seems to me that virtio-ballon case has no problem without using preloading.