> -----Original Message----- > From: Tetsuo Handa [mailto:[email protected]] > Sent: Sunday, December 17, 2017 6:22 PM > To: Wang, Wei W <[email protected]>; [email protected] > Cc: [email protected]; [email protected]; qemu- > [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; > [email protected]; [email protected]; > [email protected]; [email protected]; > [email protected]; [email protected]; > [email protected]; [email protected]; [email protected] > Subject: Re: [PATCH v19 3/7] xbitmap: add more operations > > 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.
It also mentions that the preload attempts to allocate sufficient memory to *guarantee* that the next radix tree insertion cannot fail. If we check radix_tree_node_alloc(), the comments there says "this assumes that the caller has performed appropriate preallocation". So, I think we would get a risk of triggering some issue without preload(). > > > > 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. Why is that? Best, Wei
