On Mon, May 23, 2022 at 7:54 PM Jiaqi Yan <jiaqiyan@xxxxxxxxxx> wrote:
>
> Make collapse_file roll back when copying pages failed.
> More concretely:
> * extract copying operations into a separate loop
> * postpone the updates for nr_none until both scanning and
> copying succeeded
> * postpone joining small xarray entries until both scanning and
> copying succeeded
> * postpone the update operations to NR_XXX_THPS
> * for non-SHMEM file, roll back filemap_nr_thps_inc if scan
> succeeded but copying failed
>
> Signed-off-by: Jiaqi Yan <jiaqiyan@xxxxxxxxxx>
Reviewed-by: Yang Shi <shy828301@xxxxxxxxx>
Just a nit below.
> ---
> mm/khugepaged.c | 77 ++++++++++++++++++++++++++++++-------------------
> 1 file changed, 48 insertions(+), 29 deletions(-)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 1b08e31ba081a..98976622ee7c5 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -1716,7 +1716,7 @@ static void collapse_file(struct mm_struct *mm,
> {
> struct address_space *mapping = file->f_mapping;
> gfp_t gfp;
> - struct page *new_page;
> + struct page *new_page, *page, *tmp;
> pgoff_t index, end = start + HPAGE_PMD_NR;
> LIST_HEAD(pagelist);
> XA_STATE_ORDER(xas, &mapping->i_pages, start, HPAGE_PMD_ORDER);
> @@ -1772,7 +1772,7 @@ static void collapse_file(struct mm_struct *mm,
>
> xas_set(&xas, start);
> for (index = start; index < end; index++) {
> - struct page *page = xas_next(&xas);
> + page = xas_next(&xas);
>
> VM_BUG_ON(index != xas.xa_index);
> if (is_shmem) {
> @@ -1944,10 +1944,7 @@ static void collapse_file(struct mm_struct *mm,
> }
> nr = thp_nr_pages(new_page);
>
> - if (is_shmem)
> - __mod_lruvec_page_state(new_page, NR_SHMEM_THPS, nr);
> - else {
> - __mod_lruvec_page_state(new_page, NR_FILE_THPS, nr);
> + if (!is_shmem) {
> filemap_nr_thps_inc(mapping);
> /*
> * Paired with smp_mb() in do_dentry_open() to ensure
> @@ -1958,40 +1955,44 @@ static void collapse_file(struct mm_struct *mm,
> smp_mb();
> if (inode_is_open_for_write(mapping->host)) {
> result = SCAN_FAIL;
> - __mod_lruvec_page_state(new_page, NR_FILE_THPS, -nr);
> filemap_nr_thps_dec(mapping);
> goto xa_locked;
> }
> }
>
> - if (nr_none) {
> - __mod_lruvec_page_state(new_page, NR_FILE_PAGES, nr_none);
> - if (is_shmem)
> - __mod_lruvec_page_state(new_page, NR_SHMEM, nr_none);
> - }
> -
> - /* Join all the small entries into a single multi-index entry */
> - xas_set_order(&xas, start, HPAGE_PMD_ORDER);
> - xas_store(&xas, new_page);
> xa_locked:
> xas_unlock_irq(&xas);
> xa_unlocked:
>
> if (result == SCAN_SUCCEED) {
> - struct page *page, *tmp;
> -
> /*
> * Replacing old pages with new one has succeeded, now we
> - * need to copy the content and free the old pages.
> + * attempt to copy the contents.
> */
> index = start;
> - list_for_each_entry_safe(page, tmp, &pagelist, lru) {
> + list_for_each_entry(page, &pagelist, lru) {
> while (index < page->index) {
> clear_highpage(new_page + (index % HPAGE_PMD_NR));
> index++;
> }
> - copy_highpage(new_page + (page->index % HPAGE_PMD_NR),
> - page);
> + if (copy_highpage_mc(new_page + (page->index % HPAGE_PMD_NR), page)) {
> + result = SCAN_COPY_MC;
> + break;
> + }
> + index++;
> + }
> + while (result == SCAN_SUCCEED && index < end) {
> + clear_highpage(new_page + (page->index % HPAGE_PMD_NR));
> + index++;
> + }
> + }
> +
> + if (result == SCAN_SUCCEED) {
> + /*
> + * Copying old pages to huge one has succeeded, now we
> + * need to free the old pages.
> + */
> + list_for_each_entry_safe(page, tmp, &pagelist, lru) {
> list_del(&page->lru);
> page->mapping = NULL;
> page_ref_unfreeze(page, 1);
> @@ -1999,12 +2000,23 @@ static void collapse_file(struct mm_struct *mm,
> ClearPageUnevictable(page);
> unlock_page(page);
> put_page(page);
> - index++;
> }
> - while (index < end) {
> - clear_highpage(new_page + (index % HPAGE_PMD_NR));
> - index++;
> +
> + xas_lock_irq(&xas);
> + if (is_shmem)
> + __mod_lruvec_page_state(new_page, NR_SHMEM_THPS, nr);
> + else
> + __mod_lruvec_page_state(new_page, NR_FILE_THPS, nr);
> +
> + if (nr_none) {
> + __mod_lruvec_page_state(new_page, NR_FILE_PAGES, nr_none);
> + if (is_shmem)
> + __mod_lruvec_page_state(new_page, NR_SHMEM, nr_none);
> }
> + /* Join all the small entries into a single multi-index entry. */
> + xas_set_order(&xas, start, HPAGE_PMD_ORDER);
> + xas_store(&xas, new_page);
> + xas_unlock_irq(&xas);
>
> SetPageUptodate(new_page);
> page_ref_add(new_page, HPAGE_PMD_NR - 1);
> @@ -2020,9 +2032,9 @@ static void collapse_file(struct mm_struct *mm,
>
> khugepaged_pages_collapsed++;
> } else {
> - struct page *page;
> -
> - /* Something went wrong: roll back page cache changes */
> + /*
> + * Something went wrong: roll back page cache changes
> + */
Changing from one line to multiple lines seems pointless.
> xas_lock_irq(&xas);
> mapping->nrpages -= nr_none;
>
> @@ -2055,6 +2067,13 @@ static void collapse_file(struct mm_struct *mm,
> xas_lock_irq(&xas);
> }
> VM_BUG_ON(nr_none);
> + /*
> + * Undo the updates of filemap_nr_thps_inc for non-SHMEM file only.
> + * This undo is not needed unless failure is due to SCAN_COPY_MC.
> + */
> + if (!is_shmem && result == SCAN_COPY_MC)
> + filemap_nr_thps_dec(mapping);
> +
> xas_unlock_irq(&xas);
>
> new_page->mapping = NULL;
> --
> 2.36.1.124.g0e6072fb45-goog
>
