On Tue, Oct 18, 2022 at 06:32:46PM +0500, Muhammad Usama Anjum wrote:
On 10/18/22 3:36 PM, Muhammad Usama Anjum wrote:
> > I mean we should be able to specify for what > > pages we need to get info > > for. An ioctl argument can have these four fields: > > * required bits (rmask & mask == mask) - all > > bits from this mask have to be set. > > * any of these bits (amask & mask != 0) - any of these bits is set. > > * exclude masks (emask & mask == 0) = none of these bits are set. > > * return mask - bits that have to be reported to user.
The required mask (rmask) makes sense to me. At the moment, I only know about the practical use case for the required mask. Can you share how can any and exclude masks help for the CRIU?
I looked at should_dump_page in the CRIU code: https://github.com/checkpoint-restore/criu/blob/45641ab26d7bb78706a6215fdef8...
When CRIU dumps file private mappings, it needs to get pages that have PME_PRESENT or PME_SWAP but don't have PME_FILE.
I would really like to see the mask discussed will be adopted. With it CRIU will be able to migrate huge sparse VMAs assuming that a single hole is processed in O(1) time.
Use cases for migrating sparse VMAs are binaries sanitized with ASAN, MSAN or TSAN [1]. All of these sanitizers produce sparse mappings of shadow memory [2]. Being able to migrate such binaries allows to highly reduce the amount of work needed to identify and fix post-migration crashes, which happen constantly.
Hello all,
I've included the masks which the CRIU developers have specified. max_out_page is another new optional variable which is needed to terminate the operation without visiting all the pages after finding the max_out_page number of desired pages. There is no way to terminate the operation without this variable.
How does the interface looks now? Please comment.
Updated interface with only one IOCTL. If vec is defined, get operation will be performed. If PAGEMAP_SD_CLEAR flag is specified, soft dirty bit will be cleared as well. CLEAR flag can only be specified for clearing soft dirty bit.
/* PAGEMAP IOCTL */ #define PAGEMAP_SCAN _IOWR('f', 16, struct pagemap_sd_args)
/* Bits are set in the bitmap of the page_region and masks in pagemap_sd_args */ #define PAGE_IS_SD 1 << 0 #define PAGE_IS_FILE 1 << 1 #define PAGE_IS_PRESENT 1 << 2 #define PAGE_IS_SWAPED 1 << 3
/**
- struct page_region - Page region with bitmap flags
- @start: Start of the region
- @len: Length of the region
- bitmap: Bits sets for the region
*/ struct page_region { __u64 start; __u64 len; __u64 bitmap; };
/**
- struct pagemap_sd_args - Soft-dirty IOCTL argument
- @start: Starting address of the page
- @len: Length of the region (All the pages in this length are included)
- @vec: Output page_region struct array
- @vec_len: Length of the page_region struct array
- @max_out_page: Optional max output pages (It must be less than vec_len if
specified)
- @flags: Special flags for the IOCTL
- @rmask: Required mask - All of these bits have to be set
Why have it at all if it always has to be all 1s?
- @amask: Any mask - Any of these bits are set
which ones?
- @emask: Exclude mask - None of these bits are set
Why have it, if none are ever set?
- @rmask: Bits that have to be reported to the user in page_region
I feel like I have no idea what these bits are...
Anyway, please send a real patch, with real code, so we have a better idea of what is happening. AFTER you have tested and made it all work properly.
thanks,
greg k-h