On Fri, Jul 21, 2023 at 10:50:19PM +0500, Muhammad Usama Anjum wrote:
On 7/21/23 4:23 PM, Michał Mirosław wrote:
On Fri, Jul 21, 2023 at 03:48:22PM +0500, Muhammad Usama Anjum wrote:
On 7/21/23 12:28 AM, Michał Mirosław wrote:
[...]
d. change the ioctl to be a SCAN with optional WP. Addressing the original use-case, GetWriteWatch() can be implemented as:
As I've mentioned several times previously (without the name of ResetWriteWatch()) that we need exclusive WP without GET. This could be implemented with UFFDIO_WRITEPROTECT. But when we use UFFDIO_WRITEPROTECT, we hit some special case and performance is very slow. So with UFFD WP expert, Peter Xu we have decided to put exclusive WP in this IOCTL for implementation of ResetWriteWatch().
A lot of simplification of the patch is made possible because of not keeping exclusive WP. (You have also written some quality code, more better.)
memset(&args, 0, sizeof(args)); args.start = lpBaseAddress; args.end = lpBaseAddress + dwRegionSize; args.max_pages = *lpdwCount; *lpdwGranularity = PAGE_SIZE; args.flags = PM_SCAN_CHECK_WPASYNC; if (dwFlags & WRITE_WATCH_FLAG_RESET) args.flags |= PM_SCAN_WP_MATCHED; args.categories_mask = PAGE_IS_WRITTEN; args.return_mask = PAGE_IS_WRITTEN;For ResetWriteWatch() you would:
args.flags = PM_SCAN_WP_MATCHING; args.categories_mask = PAGE_IS_WPASYNC | PAGE_IS_WRITTEN; args.return_mask = 0;
Or (if you want to error out if the range doesn't have WP enabled):
args.flags = PM_SCAN_WP_MATCHING | PM_SCAN_CHECK_WPASYNC; args.categories_mask = PAGE_IS_WRITTEN; args.return_mask = 0;
(PM_SCAN_CHECK_WPASYNC is effectively adding PAGE_IS_WPASYNC to the required categories.)
Right. But we don't want to perform GET in case of ResetWriteWatch(). It'll be wasted effort to perform GET as well when we don't care about the dirty status of the pages.
This doesn't really do GET: return_mask == 0 means that there won't be any ranges reported (and you can pass {NULL, 0} for arg.{vec, vec_len}). But I've changed the no-GET criteria to vec == NULL (requires vec_len == 0).
Is it possible for you to fix the above mentioned 3 things and send the patch for my testing: 1 Make GET optional 2 Detect partial THP WP operation and split 3 Optimization of moving this interesting logic to output() function
Please let me know if you cannot make the above fixes. I'll mix my patch version and your patch and fix these things up.
Sending as a reply.
Best Regards Michał Mirosław