On 4/14/21 3:39 PM, Mel Gorman wrote:
> Historically when freeing pages, free_one_page() assumed that callers
> had IRQs disabled and the zone->lock could be acquired with spin_lock().
> This confuses the scope of what local_lock_irq is protecting and what
> zone->lock is protecting in free_unref_page_list in particular.
>
> This patch uses spin_lock_irqsave() for the zone->lock in
> free_one_page() instead of relying on callers to have disabled
> IRQs. free_unref_page_commit() is changed to only deal with PCP pages
> protected by the local lock. free_unref_page_list() then first frees
> isolated pages to the buddy lists with free_one_page() and frees the rest
> of the pages to the PCP via free_unref_page_commit(). The end result
> is that free_one_page() is no longer depending on side-effects of
> local_lock to be correct.
>
> Note that this may incur a performance penalty while memory hot-remove
> is running but that is not a common operation.
>
> Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
A nit below:
> @@ -3294,6 +3295,7 @@ void free_unref_page_list(struct list_head *list)
> struct page *page, *next;
> unsigned long flags, pfn;
> int batch_count = 0;
> + int migratetype;
>
> /* Prepare pages for freeing */
> list_for_each_entry_safe(page, next, list, lru) {
> @@ -3301,15 +3303,28 @@ void free_unref_page_list(struct list_head *list)
> if (!free_unref_page_prepare(page, pfn))
> list_del(&page->lru);
> set_page_private(page, pfn);
Should probably move this below so we don't set private for pages that then go
through free_one_page()? Doesn't seem to be a bug, just unneccessary.
> +
> + /*
> + * Free isolated pages directly to the allocator, see
> + * comment in free_unref_page.
> + */
> + migratetype = get_pcppage_migratetype(page);
> + if (unlikely(migratetype >= MIGRATE_PCPTYPES)) {
> + if (unlikely(is_migrate_isolate(migratetype))) {
> + free_one_page(page_zone(page), page, pfn, 0,
> + migratetype, FPI_NONE);
> + list_del(&page->lru);
> + }
> + }
> }
>
> local_lock_irqsave(&pagesets.lock, flags);
> list_for_each_entry_safe(page, next, list, lru) {
> - unsigned long pfn = page_private(page);
> -
> + pfn = page_private(page);
> set_page_private(page, 0);
> + migratetype = get_pcppage_migratetype(page);
> trace_mm_page_free_batched(page);
> - free_unref_page_commit(page, pfn);
> + free_unref_page_commit(page, pfn, migratetype);
>
> /*
> * Guard against excessive IRQ disabled times when we get
>
