130     /// the amount of pages which were already initialized on page faults.
134 /// MoveToStaging copies chunks of consecutive pages next to each other on the guest memory to the
146         // Remove chunks of pages at once to reduce madvise(2) syscall.  in execute()
339     /// Clear the internal state for the pages.
341     /// When pages are removed by madvise with `MADV_DONTNEED` or `MADV_REMOVE`, userfaultfd
361         // TODO(b/269983521): Clear multiple pages in the same region at once.  in handle_page_remove()
374             // Erase the pages from the disk because the pages are removed from the guest memory.  in handle_page_remove()
381     /// Move active pages in the memory region to the staging memory.
383     /// It only moves active contents in the guest memory to the swap file and skips empty pages
384     /// (e.g. pages not touched, freed by balloon) using `lseek(2)` + `SEEK_HOLE/DATA`.
386     /// Returns the count of moved out pages.
501                 // Remove the batch of pages at once to reduce madvise(2) syscall.  in move_to_staging()
510         // Remove the final batch of pages.  in move_to_staging()
525     /// Write a chunk of consecutive pages in the staging memory to the swap file.
527     /// If there is no active pages in the staging memory, this returns `Ok(0)`.
529     /// The pages in guest memory have been moved to staging memory by [Self::move_to_staging()].
531     /// Returns the count of swapped out pages.
534     /// and `PageHandler` can continue working with a little pages leaking in staging memory or swap
535     /// file. The leaked pages are removed when vmm-swap is disabled and `PageHandler` is dropped.
549                 let pages = idx_range.end - idx_range.start;  in swap_out()  localVariable
561                 return Ok(pages);  in swap_out()
587     /// Returns count of pages copied from vmm-swap file to the guest memory.
597     /// Returns count of pages copied from staging memory to the guest memory.
607     /// Returns count of pages initialized with zero.
612     /// Returns count of pages which were already initialized on page faults.
622     /// Returns count of pages present in the staging memory.
632     /// Returns count of pages present in the swap files.
657     /// Swap in a chunk of consecutive pages from the staging memory and the swap file.
659     /// If there is no more pages present outside of the guest memory, this returns `Ok(0)`.
661     /// Returns the count of swapped in pages.
670         // Request the kernel to pre-populate the present pages in the swap file to page cache  in swap_in()
671         // background. At most 16MB of pages will be populated.  in swap_in()
672         // The threshold is to apply MADV_WILLNEED to bigger chunk of pages. The kernel populates  in swap_in()
673         // consecutive pages at once on MADV_WILLNEED.  in swap_in()
684                 let pages = idx_range.end - idx_range.start;  in swap_in()  localVariable
692                 region.swap_in_pages += pages;  in swap_in()
693                 return Ok(pages);  in swap_in()
707                     // The consecutive pages can be across regions. Swap-in pages in a region at  in swap_in()
711                 let pages = idx_range_in_file.end - idx_range_in_file.start;  in swap_in()  localVariable
719                 // Do not erase each chunk of pages from disk on swap_in. The whole file will be  in swap_in()
723                 region.swap_in_pages += pages;  in swap_in()
725                 return Ok(pages);  in swap_in()
727             // File has remaining pages, but regions has been consumed.  in swap_in()
747 /// This drops 2 types of pages in the staging memory to reduce disk write.
749 /// * Clean pages
750 ///   * The pages which have been swapped out to the disk and have not been changed.
751 ///   * Drop the pages in the staging memory and mark it as present on the swap file.
752 /// * Zero pages
753 ///   * Drop the pages in the staging memory. The pages will be UFFD_ZEROed on page fault.
758     /// The page idx range of pages which have been stored in the swap file.
765     /// Trim pages in the staging memory.
767     /// This returns the pages trimmed. This returns `None` if it traversed all pages in the staging
772     /// `max_size` - The maximum pages to be compared.
792                 // been changed, zero checking is useless, but less cost than file I/O for the pages  in trim_pages()
808                         error!("pages are mlock(2)ed while trimming");  in trim_pages()
838     /// Total trimmed clean pages.
843     /// Total trimmed zero pages.