Re: [PATCH v5 3/6] mm: make alloc_contig_range work at pageblock granularity

From: Christophe Leroy
Date: Mon Feb 14 2022 - 02:59:57 EST



Le 11/02/2022 à 17:41, Zi Yan a écrit :
> From: Zi Yan <ziy@xxxxxxxxxx>
>
> alloc_contig_range() worked at MAX_ORDER-1 granularity to avoid merging
> pageblocks with different migratetypes. It might unnecessarily convert
> extra pageblocks at the beginning and at the end of the range. Change
> alloc_contig_range() to work at pageblock granularity.
>
> Special handling is needed for free pages and in-use pages across the
> boundaries of the range specified alloc_contig_range(). Because these
> partially isolated pages causes free page accounting issues. The free
> pages will be split and freed into separate migratetype lists; the
> in-use pages will be migrated then the freed pages will be handled.
>
> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
> ---
> include/linux/page-isolation.h | 2 +-
> mm/internal.h | 3 +
> mm/memory_hotplug.c | 3 +-
> mm/page_alloc.c | 235 +++++++++++++++++++++++++--------
> mm/page_isolation.c | 33 ++++-
> 5 files changed, 211 insertions(+), 65 deletions(-)
>
> diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h
> index 4ef7be6def83..78ff940cc169 100644
> --- a/include/linux/page-isolation.h
> +++ b/include/linux/page-isolation.h
> @@ -54,7 +54,7 @@ int move_freepages_block(struct zone *zone, struct page *page,
> */
> int
> start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
> - unsigned migratetype, int flags);
> + unsigned migratetype, int flags, gfp_t gfp_flags);
>
> /*
> * Changes MIGRATE_ISOLATE to MIGRATE_MOVABLE.
> diff --git a/mm/internal.h b/mm/internal.h
> index 0d240e876831..509cbdc25992 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -319,6 +319,9 @@ isolate_freepages_range(struct compact_control *cc,
> int
> isolate_migratepages_range(struct compact_control *cc,
> unsigned long low_pfn, unsigned long end_pfn);
> +
> +int
> +isolate_single_pageblock(unsigned long boundary_pfn, gfp_t gfp_flags, int isolate_before_boundary);
> #endif
> int find_suitable_fallback(struct free_area *area, unsigned int order,
> int migratetype, bool only_stealable, bool *can_steal);
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index ce68098832aa..82406d2f3e46 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1863,7 +1863,8 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages,
> /* set above range as isolated */
> ret = start_isolate_page_range(start_pfn, end_pfn,
> MIGRATE_MOVABLE,
> - MEMORY_OFFLINE | REPORT_FAILURE);
> + MEMORY_OFFLINE | REPORT_FAILURE,
> + GFP_USER | __GFP_MOVABLE | __GFP_RETRY_MAYFAIL);
> if (ret) {
> reason = "failure to isolate range";
> goto failed_removal_pcplists_disabled;
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 62ef78f3d771..7a4fa21aea5c 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -8985,7 +8985,7 @@ static inline void alloc_contig_dump_pages(struct list_head *page_list)
> #endif
>
> /* [start, end) must belong to a single zone. */
> -static int __alloc_contig_migrate_range(struct compact_control *cc,
> +int __alloc_contig_migrate_range(struct compact_control *cc,
> unsigned long start, unsigned long end)
> {
> /* This function is based on compact_zone() from compaction.c. */
> @@ -9043,6 +9043,167 @@ static int __alloc_contig_migrate_range(struct compact_control *cc,
> return 0;
> }
>
> +/**
> + * split_free_page() -- split a free page at split_pfn_offset
> + * @free_page: the original free page
> + * @order: the order of the page
> + * @split_pfn_offset: split offset within the page
> + *
> + * It is used when the free page crosses two pageblocks with different migratetypes
> + * at split_pfn_offset within the page. The split free page will be put into
> + * separate migratetype lists afterwards. Otherwise, the function achieves
> + * nothing.
> + */
> +static inline void split_free_page(struct page *free_page,
> + int order, unsigned long split_pfn_offset)
> +{
> + struct zone *zone = page_zone(free_page);
> + unsigned long free_page_pfn = page_to_pfn(free_page);
> + unsigned long pfn;
> + unsigned long flags;
> + int free_page_order;
> +
> + spin_lock_irqsave(&zone->lock, flags);
> + del_page_from_free_list(free_page, zone, order);
> + for (pfn = free_page_pfn;
> + pfn < free_page_pfn + (1UL << order);) {
> + int mt = get_pfnblock_migratetype(pfn_to_page(pfn), pfn);
> +
> + free_page_order = order_base_2(split_pfn_offset);
> + __free_one_page(pfn_to_page(pfn), pfn, zone, free_page_order,
> + mt, FPI_NONE);
> + pfn += 1UL << free_page_order;
> + split_pfn_offset -= (1UL << free_page_order);
> + /* we have done the first part, now switch to second part */
> + if (split_pfn_offset == 0)
> + split_pfn_offset = (1UL << order) - (pfn - free_page_pfn);
> + }
> + spin_unlock_irqrestore(&zone->lock, flags);
> +}
> +
> +/**
> + * isolate_single_pageblock() -- tries to isolate a pageblock that might be
> + * within a free or in-use page.
> + * @boundary_pfn: pageblock-aligned pfn that a page might cross
> + * @gfp_flags: GFP flags used for migrating pages
> + * @isolate_before_boundary: isolate the pageblock before (1) or after (0)
> + * the boundary_pfn
> + *
> + * Free and in-use pages can be as big as MAX_ORDER-1 and contain more than one
> + * pageblock. When not all pageblocks within a page are isolated at the same
> + * time, free page accounting can go wrong. For example, in the case of
> + * MAX_ORDER-1 = pageblock_order + 1, a MAX_ORDER-1 page has two pagelbocks.
> + * [ MAX_ORDER-1 ]
> + * [ pageblock0 | pageblock1 ]
> + * When either pageblock is isolated, if it is a free page, the page is not
> + * split into separate migratetype lists, which is supposed to; if it is an
> + * in-use page and freed later, __free_one_page() does not split the free page
> + * either. The function handles this by splitting the free page or migrating
> + * the in-use page then splitting the free page.
> + */
> +int isolate_single_pageblock(unsigned long boundary_pfn, gfp_t gfp_flags,
> + int isolate_before_boundary)

Do you need such big param name ?

See
https://www.kernel.org/doc/html/latest/process/coding-style.html?highlight=style#naming

isolate_before_boundary could probably be shorter.

And should be a bool by the way.

> +{
> + unsigned char saved_mt;
> + /*
> + * scan at max(MAX_ORDER_NR_PAGES, pageblock_nr_pages) aligned range to
> + * avoid isolate pageblocks belonging to a bigger free or in-use page
> + */
> + unsigned long start_pfn = pfn_max_align_down(boundary_pfn);
> + unsigned long isolated_pageblock_pfn;

Variable name too long.

> + unsigned long pfn;
> +
> + VM_BUG_ON(!IS_ALIGNED(boundary_pfn, pageblock_nr_pages));
> +
> + if (isolate_before_boundary)
> + isolated_pageblock_pfn = boundary_pfn - pageblock_nr_pages;
> + else
> + isolated_pageblock_pfn = boundary_pfn;
> +
> + saved_mt = get_pageblock_migratetype(pfn_to_page(isolated_pageblock_pfn));
> + set_pageblock_migratetype(pfn_to_page(isolated_pageblock_pfn), MIGRATE_ISOLATE);
> +
> + for (pfn = start_pfn; pfn < boundary_pfn;) {

This loop is a bit long a deep. Isn't there a way to put what's in "if
(PageHuge(page) || PageTransCompound(page))" into a sub-function ?

See
https://www.kernel.org/doc/html/latest/process/coding-style.html?highlight=style#functions

> + struct page *page = pfn_to_page(pfn);
> +
> + /*
> + * start_pfn is max(MAX_ORDER_NR_PAGES, pageblock_nr_pages)
> + * aligned, if there is any free pages in [start_pfn, boundary_pfn),
> + * its head page will always be in the range.
> + */
> + if (PageBuddy(page)) {
> + int order = buddy_order(page);
> +
> + if (pfn + (1UL << order) > boundary_pfn)
> + split_free_page(page, order, boundary_pfn - pfn);
> + pfn += (1UL << order);
> + continue;
> + }
> + /*
> + * migrate compound pages then let the free page handling code
> + * above do the rest
> + */
> + if (PageHuge(page) || PageTransCompound(page)) {
> + unsigned long nr_pages = compound_nr(page);
> + int order = compound_order(page);
> + struct page *head = compound_head(page);
> + unsigned long head_pfn = page_to_pfn(head);
> +
> + if (head_pfn + nr_pages >= boundary_pfn) {
> + int ret;
> + struct compact_control cc = {
> + .nr_migratepages = 0,
> + .order = -1,
> + .zone = page_zone(pfn_to_page(head_pfn)),
> + .mode = MIGRATE_SYNC,
> + .ignore_skip_hint = true,
> + .no_set_skip_hint = true,
> + .gfp_mask = current_gfp_context(gfp_flags),
> + .alloc_contig = true,
> + };
> +
> + INIT_LIST_HEAD(&cc.migratepages);
> +
> + ret = __alloc_contig_migrate_range(&cc, head_pfn,
> + head_pfn + nr_pages);
> +
> + if (ret) {
> + /* restore the original migratetype */
> + set_pageblock_migratetype(
> + pfn_to_page(isolated_pageblock_pfn),
> + saved_mt);
> + return -EBUSY;
> + }
> + /*
> + * reset pfn, let the free page handling code
> + * above split the free page to the right
> + * migratetype list.
> + *
> + * head_pfn is not used here as a hugetlb page
> + * order can be bigger than MAX_ORDER-1, but
> + * after it is freed, the free page order is not.
> + * Use pfn within the range to find the head of
> + * the free page and reset order to 0 if a hugetlb
> + * page with >MAX_ORDER-1 order is encountered.
> + */
> + if (order > MAX_ORDER-1)
> + order = 0;
> + while (!PageBuddy(pfn_to_page(pfn))) {
> + order++;
> + pfn &= ~0UL << order;
> + }
> + continue;
> + }
> + pfn += nr_pages;
> + continue;
> + }
> +
> + pfn++;
> + }
> + return 0;
> +}
> +
> +
> /**
> * alloc_contig_range() -- tries to allocate given range of pages
> * @start: start PFN to allocate
> @@ -9067,8 +9228,9 @@ static int __alloc_contig_migrate_range(struct compact_control *cc,
> int alloc_contig_range(unsigned long start, unsigned long end,
> unsigned migratetype, gfp_t gfp_mask)
> {
> - unsigned long outer_start, outer_end;
> - unsigned int order;
> + unsigned long outer_end;
> + unsigned long alloc_start = ALIGN_DOWN(start, pageblock_nr_pages);
> + unsigned long alloc_end = ALIGN(end, pageblock_nr_pages);
> int ret = 0;
>
> struct compact_control cc = {
> @@ -9087,14 +9249,11 @@ int alloc_contig_range(unsigned long start, unsigned long end,
> * What we do here is we mark all pageblocks in range as
> * MIGRATE_ISOLATE. Because pageblock and max order pages may
> * have different sizes, and due to the way page allocator
> - * work, we align the range to biggest of the two pages so
> - * that page allocator won't try to merge buddies from
> - * different pageblocks and change MIGRATE_ISOLATE to some
> - * other migration type.
> + * work, start_isolate_page_range() has special handlings for this.
> *
> * Once the pageblocks are marked as MIGRATE_ISOLATE, we
> * migrate the pages from an unaligned range (ie. pages that
> - * we are interested in). This will put all the pages in
> + * we are interested in). This will put all the pages in
> * range back to page allocator as MIGRATE_ISOLATE.
> *
> * When this is done, we take the pages in range from page
> @@ -9107,9 +9266,9 @@ int alloc_contig_range(unsigned long start, unsigned long end,
> * put back to page allocator so that buddy can use them.
> */
>
> - ret = start_isolate_page_range(start, end, migratetype, 0);
> + ret = start_isolate_page_range(start, end, migratetype, 0, gfp_mask);
> if (ret)
> - return ret;
> + goto done;
>
> drain_all_pages(cc.zone);
>
> @@ -9128,68 +9287,28 @@ int alloc_contig_range(unsigned long start, unsigned long end,
> goto done;
> ret = 0;
>
> - /*
> - * Pages from [start, end) are within a MAX_ORDER_NR_PAGES
> - * aligned blocks that are marked as MIGRATE_ISOLATE. What's
> - * more, all pages in [start, end) are free in page allocator.
> - * What we are going to do is to allocate all pages from
> - * [start, end) (that is remove them from page allocator).
> - *
> - * The only problem is that pages at the beginning and at the
> - * end of interesting range may be not aligned with pages that
> - * page allocator holds, ie. they can be part of higher order
> - * pages. Because of this, we reserve the bigger range and
> - * once this is done free the pages we are not interested in.
> - *
> - * We don't have to hold zone->lock here because the pages are
> - * isolated thus they won't get removed from buddy.
> - */
> -
> - order = 0;
> - outer_start = start;
> - while (!PageBuddy(pfn_to_page(outer_start))) {
> - if (++order >= MAX_ORDER) {
> - outer_start = start;
> - break;
> - }
> - outer_start &= ~0UL << order;
> - }
> -
> - if (outer_start != start) {
> - order = buddy_order(pfn_to_page(outer_start));
> -
> - /*
> - * outer_start page could be small order buddy page and
> - * it doesn't include start page. Adjust outer_start
> - * in this case to report failed page properly
> - * on tracepoint in test_pages_isolated()
> - */
> - if (outer_start + (1UL << order) <= start)
> - outer_start = start;
> - }
> -
> /* Make sure the range is really isolated. */
> - if (test_pages_isolated(outer_start, end, 0)) {
> + if (test_pages_isolated(alloc_start, alloc_end, 0)) {
> ret = -EBUSY;
> goto done;
> }
>
> /* Grab isolated pages from freelists. */
> - outer_end = isolate_freepages_range(&cc, outer_start, end);
> + outer_end = isolate_freepages_range(&cc, alloc_start, alloc_end);
> if (!outer_end) {
> ret = -EBUSY;
> goto done;
> }
>
> /* Free head and tail (if any) */
> - if (start != outer_start)
> - free_contig_range(outer_start, start - outer_start);
> - if (end != outer_end)
> - free_contig_range(end, outer_end - end);
> + if (start != alloc_start)
> + free_contig_range(alloc_start, start - alloc_start);
> + if (end != alloc_end)
> + free_contig_range(end, alloc_end - end);
>
> done:
> - undo_isolate_page_range(pfn_max_align_down(start),
> - pfn_max_align_up(end), migratetype);
> + undo_isolate_page_range(alloc_start,
> + alloc_end, migratetype);
> return ret;
> }
> EXPORT_SYMBOL(alloc_contig_range);
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index 64d093ab83ec..0256d5e1032c 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -285,6 +285,8 @@ __first_valid_page(unsigned long pfn, unsigned long nr_pages)
> * and PageOffline() pages.
> * REPORT_FAILURE - report details about the failure to
> * isolate the range
> + * @gfp_flags: GFP flags used for migrating pages that sit across the
> + * range boundaries.
> *
> * Making page-allocation-type to be MIGRATE_ISOLATE means free pages in
> * the range will never be allocated. Any free pages and pages freed in the
> @@ -293,6 +295,10 @@ __first_valid_page(unsigned long pfn, unsigned long nr_pages)
> * pages in the range finally, the caller have to free all pages in the range.
> * test_page_isolated() can be used for test it.
> *
> + * The function first tries to isolate the pageblocks at the beginning and end
> + * of the range, since there might be pages across the range boundaries.
> + * Afterwards, it isolates the rest of the range.
> + *
> * There is no high level synchronization mechanism that prevents two threads
> * from trying to isolate overlapping ranges. If this happens, one thread
> * will notice pageblocks in the overlapping range already set to isolate.
> @@ -313,21 +319,38 @@ __first_valid_page(unsigned long pfn, unsigned long nr_pages)
> * Return: 0 on success and -EBUSY if any part of range cannot be isolated.
> */
> int start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
> - unsigned migratetype, int flags)
> + unsigned migratetype, int flags, gfp_t gfp_flags)
> {
> unsigned long pfn;
> struct page *page;
> + /* isolation is done at page block granularity */
> + unsigned long isolate_start = ALIGN_DOWN(start_pfn, pageblock_nr_pages);
> + unsigned long isolate_end = ALIGN(end_pfn, pageblock_nr_pages);
> + int ret;
>
> - unsigned long isolate_start = pfn_max_align_down(start_pfn);
> - unsigned long isolate_end = pfn_max_align_up(end_pfn);
> + /* isolate [isolate_start, isolate_start + pageblock_nr_pages] pageblock */
> + ret = isolate_single_pageblock(isolate_start, gfp_flags, 0);
> + if (ret)
> + return ret;
> +
> + /* isolate [isolate_end - pageblock_nr_pages, isolate_end] pageblock */
> + ret = isolate_single_pageblock(isolate_end, gfp_flags, 1);
> + if (ret) {
> + unset_migratetype_isolate(pfn_to_page(isolate_start), migratetype);
> + return ret;
> + }
>
> - for (pfn = isolate_start;
> - pfn < isolate_end;
> + /* skip isolated pageblocks at the beginning and end */
> + for (pfn = isolate_start + pageblock_nr_pages;
> + pfn < isolate_end - pageblock_nr_pages;
> pfn += pageblock_nr_pages) {
> page = __first_valid_page(pfn, pageblock_nr_pages);
> if (page && set_migratetype_isolate(page, migratetype, flags,
> start_pfn, end_pfn)) {
> undo_isolate_page_range(isolate_start, pfn, migratetype);
> + unset_migratetype_isolate(
> + pfn_to_page(isolate_end - pageblock_nr_pages),
> + migratetype);
> return -EBUSY;
> }
> }