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Message-ID: <46f29fba-d35-c6a-74d0-38dc6aa15f15@google.com>
Date: Thu, 23 Mar 2023 12:51:52 -0700 (PDT)
From: Hugh Dickins <hughd@...gle.com>
To: David Stevens <stevensd@...omium.org>
cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
Peter Xu <peterx@...hat.com>,
Matthew Wilcox <willy@...radead.org>,
"Kirill A . Shutemov" <kirill@...temov.name>,
Yang Shi <shy828301@...il.com>,
David Hildenbrand <david@...hat.com>,
Hugh Dickins <hughd@...gle.com>,
Jiaqi Yan <jiaqiyan@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 1/3] mm/khugepaged: refactor collapse_file control
flow
On Tue, 7 Mar 2023, David Stevens wrote:
> From: David Stevens <stevensd@...omium.org>
>
> Add a rollback label to deal with failure, instead of continuously
> checking for RESULT_SUCCESS, to make it easier to add more failure
> cases. The refactoring also allows the collapse_file tracepoint to
> include hpage on success (instead of NULL).
>
> Signed-off-by: David Stevens <stevensd@...omium.org>
> Acked-by: Peter Xu <peterx@...hat.com>
> Reviewed-by: Yang Shi <shy828301@...il.com>
This one looks like a nice de-indentation to me,
even if it's not followed by 2/3 and 3/3.
Acked-by: Hugh Dickins <hughd@...gle.com>
> ---
> mm/khugepaged.c | 219 ++++++++++++++++++++++++------------------------
> 1 file changed, 108 insertions(+), 111 deletions(-)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 3ea2aa55c2c5..b954e3c685e7 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -1907,6 +1907,12 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
> if (result != SCAN_SUCCEED)
> goto out;
>
> + __SetPageLocked(hpage);
> + if (is_shmem)
> + __SetPageSwapBacked(hpage);
> + hpage->index = start;
> + hpage->mapping = mapping;
> +
> /*
> * Ensure we have slots for all the pages in the range. This is
> * almost certainly a no-op because most of the pages must be present
> @@ -1919,16 +1925,10 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
> xas_unlock_irq(&xas);
> if (!xas_nomem(&xas, GFP_KERNEL)) {
> result = SCAN_FAIL;
> - goto out;
> + goto rollback;
> }
> } while (1);
>
> - __SetPageLocked(hpage);
> - if (is_shmem)
> - __SetPageSwapBacked(hpage);
> - hpage->index = start;
> - hpage->mapping = mapping;
> -
> /*
> * At this point the hpage is locked and not up-to-date.
> * It's safe to insert it into the page cache, because nobody would
> @@ -2145,129 +2145,126 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
> */
> try_to_unmap_flush();
>
> - if (result == SCAN_SUCCEED) {
> - /*
> - * Replacing old pages with new one has succeeded, now we
> - * attempt to copy the contents.
> - */
> - index = start;
> - list_for_each_entry(page, &pagelist, lru) {
> - while (index < page->index) {
> - clear_highpage(hpage + (index % HPAGE_PMD_NR));
> - index++;
> - }
> - if (copy_mc_highpage(hpage + (page->index % HPAGE_PMD_NR),
> - page) > 0) {
> - result = SCAN_COPY_MC;
> - break;
> - }
> - index++;
> - }
> - while (result == SCAN_SUCCEED && index < end) {
> + if (result != SCAN_SUCCEED)
> + goto rollback;
> +
> + /*
> + * Replacing old pages with new one has succeeded, now we
> + * attempt to copy the contents.
> + */
> + index = start;
> + list_for_each_entry(page, &pagelist, lru) {
> + while (index < page->index) {
> clear_highpage(hpage + (index % HPAGE_PMD_NR));
> index++;
> }
> + if (copy_mc_highpage(hpage + (page->index % HPAGE_PMD_NR), page) > 0) {
> + result = SCAN_COPY_MC;
> + goto rollback;
> + }
> + index++;
> + }
> + while (index < end) {
> + clear_highpage(hpage + (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);
> - ClearPageActive(page);
> - ClearPageUnevictable(page);
> - unlock_page(page);
> - put_page(page);
> - }
> + /*
> + * 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);
> + ClearPageActive(page);
> + ClearPageUnevictable(page);
> + unlock_page(page);
> + put_page(page);
> + }
>
> - xas_lock_irq(&xas);
> - if (is_shmem)
> - __mod_lruvec_page_state(hpage, NR_SHMEM_THPS, nr);
> - else
> - __mod_lruvec_page_state(hpage, NR_FILE_THPS, nr);
> + xas_lock_irq(&xas);
> + if (is_shmem)
> + __mod_lruvec_page_state(hpage, NR_SHMEM_THPS, nr);
> + else
> + __mod_lruvec_page_state(hpage, NR_FILE_THPS, nr);
>
> - if (nr_none) {
> - __mod_lruvec_page_state(hpage, NR_FILE_PAGES, nr_none);
> - /* nr_none is always 0 for non-shmem. */
> - __mod_lruvec_page_state(hpage, 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, hpage);
> - xas_unlock_irq(&xas);
> + if (nr_none) {
> + __mod_lruvec_page_state(hpage, NR_FILE_PAGES, nr_none);
> + /* nr_none is always 0 for non-shmem. */
> + __mod_lruvec_page_state(hpage, 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, hpage);
> + xas_unlock_irq(&xas);
>
> - folio = page_folio(hpage);
> - folio_mark_uptodate(folio);
> - folio_ref_add(folio, HPAGE_PMD_NR - 1);
> + folio = page_folio(hpage);
> + folio_mark_uptodate(folio);
> + folio_ref_add(folio, HPAGE_PMD_NR - 1);
>
> - if (is_shmem)
> - folio_mark_dirty(folio);
> - folio_add_lru(folio);
> + if (is_shmem)
> + folio_mark_dirty(folio);
> + folio_add_lru(folio);
>
> - /*
> - * Remove pte page tables, so we can re-fault the page as huge.
> - */
> - result = retract_page_tables(mapping, start, mm, addr, hpage,
> - cc);
> - unlock_page(hpage);
> - hpage = NULL;
> - } else {
> - /* Something went wrong: roll back page cache changes */
> - xas_lock_irq(&xas);
> - if (nr_none) {
> - mapping->nrpages -= nr_none;
> - shmem_uncharge(mapping->host, nr_none);
> + /*
> + * Remove pte page tables, so we can re-fault the page as huge.
> + */
> + result = retract_page_tables(mapping, start, mm, addr, hpage,
> + cc);
> + unlock_page(hpage);
> + goto out;
> +
> +rollback:
> + /* Something went wrong: roll back page cache changes */
> + xas_lock_irq(&xas);
> + if (nr_none) {
> + mapping->nrpages -= nr_none;
> + shmem_uncharge(mapping->host, nr_none);
> + }
> +
> + xas_set(&xas, start);
> + xas_for_each(&xas, page, end - 1) {
> + page = list_first_entry_or_null(&pagelist,
> + struct page, lru);
> + if (!page || xas.xa_index < page->index) {
> + if (!nr_none)
> + break;
> + nr_none--;
> + /* Put holes back where they were */
> + xas_store(&xas, NULL);
> + continue;
> }
>
> - xas_set(&xas, start);
> - xas_for_each(&xas, page, end - 1) {
> - page = list_first_entry_or_null(&pagelist,
> - struct page, lru);
> - if (!page || xas.xa_index < page->index) {
> - if (!nr_none)
> - break;
> - nr_none--;
> - /* Put holes back where they were */
> - xas_store(&xas, NULL);
> - continue;
> - }
> + VM_BUG_ON_PAGE(page->index != xas.xa_index, page);
>
> - VM_BUG_ON_PAGE(page->index != xas.xa_index, page);
> + /* Unfreeze the page. */
> + list_del(&page->lru);
> + page_ref_unfreeze(page, 2);
> + xas_store(&xas, page);
> + xas_pause(&xas);
> + xas_unlock_irq(&xas);
> + unlock_page(page);
> + putback_lru_page(page);
> + 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);
>
> - /* Unfreeze the page. */
> - list_del(&page->lru);
> - page_ref_unfreeze(page, 2);
> - xas_store(&xas, page);
> - xas_pause(&xas);
> - xas_unlock_irq(&xas);
> - unlock_page(page);
> - putback_lru_page(page);
> - 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);
>
> - xas_unlock_irq(&xas);
> + hpage->mapping = NULL;
>
> - hpage->mapping = NULL;
> - }
> + unlock_page(hpage);
> + put_page(hpage);
>
> - if (hpage)
> - unlock_page(hpage);
> out:
> VM_BUG_ON(!list_empty(&pagelist));
> - if (hpage)
> - put_page(hpage);
> -
> trace_mm_khugepaged_collapse_file(mm, hpage, index, is_shmem, addr, file, nr, result);
> return result;
> }
> --
> 2.40.0.rc0.216.gc4246ad0f0-goog
>
>
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