On Fri, 16 Jun 2023 at 08:57, Muhammad Usama Anjum <usama.anjum@xxxxxxxxxxxxx> wrote: > > On 6/16/23 1:07 AM, Michał Mirosław wrote: > > On Thu, 15 Jun 2023 at 17:11, Muhammad Usama Anjum > > <usama.anjum@xxxxxxxxxxxxx> wrote: > >> On 6/15/23 7:52 PM, Michał Mirosław wrote: > >>> On Thu, 15 Jun 2023 at 15:58, Muhammad Usama Anjum > >>> <usama.anjum@xxxxxxxxxxxxx> wrote: > >>>> I'll send next revision now. > >>>> On 6/14/23 11:00 PM, Michał Mirosław wrote: > >>>>> (A quick reply to answer open questions in case they help the next version.) [...] > >>>>> I guess this will be reworked anyway, but I'd prefer this didn't need > >>>>> custom errors etc. If we agree to decoupling the selection and GET > >>>>> output, it could be: > >>>>> > >>>>> bool is_interesting_page(p, flags); // this one does the > >>>>> required/anyof/excluded match > >>>>> size_t output_range(p, start, len, flags); // this one fills the > >>>>> output vector and returns how many pages were fit > >>>>> > >>>>> In this setup, `is_interesting_page() && (n_out = output_range()) < > >>>>> n_pages` means this is the final range, no more will fit. And if > >>>>> `n_out == 0` then no pages fit and no WP is needed (no other special > >>>>> cases). > >>>> Right now, pagemap_scan_output() performs the work of both of these two > >>>> functions. The part can be broken into is_interesting_pages() and we can > >>>> leave the remaining part as it is. > >>>> > >>>> Saying that n_out < n_pages tells us the buffer is full covers one case. > >>>> But there is case of maximum pages have been found and walk needs to be > >>>> aborted. > >>> > >>> This case is exactly what `n_out < n_pages` will cover (if scan_output > >>> uses max_pages properly to limit n_out). > >>> Isn't it that when the buffer is full we want to abort the scan always > >>> (with WP if `n_out > 0`)? > >> Wouldn't it be duplication of condition if buffer is full inside > >> pagemap_scan_output() and just outside it. Inside pagemap_scan_output() we > >> check if we have space before putting data inside it. I'm using this same > >> condition to indicate that buffer is full. > > > > I'm not sure what do you mean? The buffer-full conditions would be > > checked in ..scan_output() and communicated to the caller by returning > > N less than `n_pages` passed in. This is exactly how e.g. read() > > works: if you get less than requested you've hit the end of the file. > > If the file happens to have size that is equal to the provided buffer > > length, the next read() will return 0. > Right now we have: > > pagemap_scan_output(): > if (p->vec_buf_index >= p->vec_buf_len) > return PM_SCAN_BUFFER_FULL; > if (p->found_pages == p->max_pages) > return PM_SCAN_FOUND_MAX_PAGES; Why do you need to differentiate between those cases? > pagemap_scan_pmd_entry(): > ret = pagemap_scan_output(bitmap, p, start, n_pages); > if (ret >= 0) // success > make_UFFD_WP and flush > else > buffer_error > > You are asking me to do: > > pagemap_scan_output(): > if (p->vec_buf_index >= p->vec_buf_len) > return 0; > if (p->found_pages == p->max_pages) > return PM_SCAN_FOUND_MAX_PAGES; This should be instead: n_pages = min(p->max_pags - p_found_pages, n_pages) ... return n_pages; > pagemap_scan_pmd_entry(): > ret = pagemap_scan_output(bitmap, p, start, n_pages); > if (ret > 0) // success > make_UFFD_WP and flush > else if (ret == 0) // buffer full > return PM_SCAN_BUFFER_FULL; > else //other errors > buffer_error And this would be: if (ret > 0 && WP) WP + flush if (ret < n_pages) return -ENOSPC; > So you are asking me to go from consie code to write more lines of code. I > would write more lines without any issue if it improves readability and > logical sense. But I don't see here any benefit. Please see the clarifications above. Best Regards Michał Mirosław
