> On Feb 25, 2021, at 4:16 AM, Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > On Wed, Feb 24, 2021 at 11:29:04PM -0800, Nadav Amit wrote: >> Just as applications can use prefetch instructions to overlap >> computations and memory accesses, applications may want to overlap the >> page-faults and compute or overlap the I/O accesses that are required >> for page-faults of different pages. > > Isn't this madvise(MADV_WILLNEED)? Good point that I should have mentioned. In a way prefetch_page() a combination of mincore() and MADV_WILLNEED. There are 4 main differences from MADV_WILLNEED: 1. Much lower invocation cost if the readahead is not needed: this allows to prefetch pages more abundantly. 2. Return value: return value tells you whether the page is accessible. This makes it usable for coroutines, for instance. In this regard the call is more similar to mincore() than MADV_WILLNEED. 3. The PTEs are mapped if the pages are already present in the swap/page-cache, preventing an additional page-fault just to map them. 4. Avoiding heavy-weight reclamation on low memory (this may need to be selective, and can be integrated with MADV_WILLNEED).
