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Date: Thu, 25 Apr 2019 19:08:17 +0000
From: Nadav Amit <namit@...are.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
CC: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Arnd Bergmann <arnd@...db.de>,
Julien Freche <jfreche@...are.com>,
Pv-drivers <Pv-drivers@...are.com>,
Jason Wang <jasowang@...hat.com>,
LKML <linux-kernel@...r.kernel.org>,
"virtualization@...ts.linux-foundation.org"
<virtualization@...ts.linux-foundation.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH v3 1/4] mm/balloon_compaction: list interfaces
> On Apr 24, 2019, at 6:49 AM, Michael S. Tsirkin <mst@...hat.com> wrote:
>
> On Tue, Apr 23, 2019 at 04:45:28PM -0700, Nadav Amit wrote:
>> Introduce interfaces for ballooning enqueueing and dequeueing of a list
>> of pages. These interfaces reduce the overhead of storing and restoring
>> IRQs by batching the operations. In addition they do not panic if the
>> list of pages is empty.
>>
>> Cc: "Michael S. Tsirkin" <mst@...hat.com>
>> Cc: Jason Wang <jasowang@...hat.com>
>> Cc: linux-mm@...ck.org
>> Cc: virtualization@...ts.linux-foundation.org
>> Reviewed-by: Xavier Deguillard <xdeguillard@...are.com>
>> Signed-off-by: Nadav Amit <namit@...are.com>
>
>
> Looks good overall. Two minor comments below.
>
>
>> ---
>> include/linux/balloon_compaction.h | 4 +
>> mm/balloon_compaction.c | 144 +++++++++++++++++++++--------
>> 2 files changed, 110 insertions(+), 38 deletions(-)
>>
>> diff --git a/include/linux/balloon_compaction.h b/include/linux/balloon_compaction.h
>> index f111c780ef1d..430b6047cef7 100644
>> --- a/include/linux/balloon_compaction.h
>> +++ b/include/linux/balloon_compaction.h
>> @@ -64,6 +64,10 @@ extern struct page *balloon_page_alloc(void);
>> extern void balloon_page_enqueue(struct balloon_dev_info *b_dev_info,
>> struct page *page);
>> extern struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info);
>> +extern size_t balloon_page_list_enqueue(struct balloon_dev_info *b_dev_info,
>> + struct list_head *pages);
>> +extern size_t balloon_page_list_dequeue(struct balloon_dev_info *b_dev_info,
>> + struct list_head *pages, size_t n_req_pages);
>>
>> static inline void balloon_devinfo_init(struct balloon_dev_info *balloon)
>> {
>> diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
>> index ef858d547e2d..a2995002edc2 100644
>> --- a/mm/balloon_compaction.c
>> +++ b/mm/balloon_compaction.c
>> @@ -10,6 +10,105 @@
>> #include <linux/export.h>
>> #include <linux/balloon_compaction.h>
>>
>> +static void balloon_page_enqueue_one(struct balloon_dev_info *b_dev_info,
>> + struct page *page)
>> +{
>> + /*
>> + * Block others from accessing the 'page' when we get around to
>> + * establishing additional references. We should be the only one
>> + * holding a reference to the 'page' at this point. If we are not, then
>> + * memory corruption is possible and we should stop execution.
>> + */
>> + BUG_ON(!trylock_page(page));
>> + list_del(&page->lru);
>> + balloon_page_insert(b_dev_info, page);
>> + unlock_page(page);
>> + __count_vm_event(BALLOON_INFLATE);
>> +}
>> +
>> +/**
>> + * balloon_page_list_enqueue() - inserts a list of pages into the balloon page
>> + * list.
>> + * @b_dev_info: balloon device descriptor where we will insert a new page to
>> + * @pages: pages to enqueue - allocated using balloon_page_alloc.
>> + *
>> + * Driver must call it to properly enqueue a balloon pages before definitively
>> + * removing it from the guest system.
>> + *
>> + * Return: number of pages that were enqueued.
>> + */
>> +size_t balloon_page_list_enqueue(struct balloon_dev_info *b_dev_info,
>> + struct list_head *pages)
>> +{
>> + struct page *page, *tmp;
>> + unsigned long flags;
>> + size_t n_pages = 0;
>> +
>> + spin_lock_irqsave(&b_dev_info->pages_lock, flags);
>> + list_for_each_entry_safe(page, tmp, pages, lru) {
>> + balloon_page_enqueue_one(b_dev_info, page);
>> + n_pages++;
>> + }
>> + spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
>> + return n_pages;
>> +}
>> +EXPORT_SYMBOL_GPL(balloon_page_list_enqueue);
>> +
>> +/**
>> + * balloon_page_list_dequeue() - removes pages from balloon's page list and
>> + * returns a list of the pages.
>> + * @b_dev_info: balloon device decriptor where we will grab a page from.
>> + * @pages: pointer to the list of pages that would be returned to the caller.
>> + * @n_req_pages: number of requested pages.
>> + *
>> + * Driver must call this function to properly de-allocate a previous enlisted
>> + * balloon pages before definetively releasing it back to the guest system.
>> + * This function tries to remove @n_req_pages from the ballooned pages and
>> + * return them to the caller in the @pages list.
>> + *
>> + * Note that this function may fail to dequeue some pages temporarily empty due
>> + * to compaction isolated pages.
>> + *
>> + * Return: number of pages that were added to the @pages list.
>> + */
>> +size_t balloon_page_list_dequeue(struct balloon_dev_info *b_dev_info,
>> + struct list_head *pages, size_t n_req_pages)
>> +{
>> + struct page *page, *tmp;
>> + unsigned long flags;
>> + size_t n_pages = 0;
>> +
>> + spin_lock_irqsave(&b_dev_info->pages_lock, flags);
>> + list_for_each_entry_safe(page, tmp, &b_dev_info->pages, lru) {
>> + if (n_pages == n_req_pages)
>> + break;
>> +
>> + /*
>> + * Block others from accessing the 'page' while we get around
>
> should be "get around to" - same as in other places
>
>
>> + * establishing additional references and preparing the 'page'
>> + * to be released by the balloon driver.
>> + */
>> + if (!trylock_page(page))
>> + continue;
>> +
>> + if (IS_ENABLED(CONFIG_BALLOON_COMPACTION) &&
>> + PageIsolated(page)) {
>> + /* raced with isolation */
>> + unlock_page(page);
>> + continue;
>> + }
>> + balloon_page_delete(page);
>> + __count_vm_event(BALLOON_DEFLATE);
>> + unlock_page(page);
>> + list_add(&page->lru, pages);
>
> I'm not sure whether this list_add must be under the page lock,
> but enqueue does list_del under page lock, so I think it's
> a good idea to keep dequeue consistent, operating in the
> reverse order of enqueue.
>
>> + ++n_pages;
>> + }
>> + spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
>> +
>> + return n_pages;
>> +}
>> +EXPORT_SYMBOL_GPL(balloon_page_list_dequeue);
>> +
>> /*
>> * balloon_page_alloc - allocates a new page for insertion into the balloon
>> * page list.
>> @@ -43,17 +142,9 @@ void balloon_page_enqueue(struct balloon_dev_info *b_dev_info,
>> {
>> unsigned long flags;
>>
>> - /*
>> - * Block others from accessing the 'page' when we get around to
>> - * establishing additional references. We should be the only one
>> - * holding a reference to the 'page' at this point.
>> - */
>> - BUG_ON(!trylock_page(page));
>> spin_lock_irqsave(&b_dev_info->pages_lock, flags);
>> - balloon_page_insert(b_dev_info, page);
>> - __count_vm_event(BALLOON_INFLATE);
>> + balloon_page_enqueue_one(b_dev_info, page);
>> spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
>> - unlock_page(page);
>> }
>> EXPORT_SYMBOL_GPL(balloon_page_enqueue);
>>
>> @@ -70,36 +161,13 @@ EXPORT_SYMBOL_GPL(balloon_page_enqueue);
>> */
>> struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
>> {
>> - struct page *page, *tmp;
>> unsigned long flags;
>> - bool dequeued_page;
>> + LIST_HEAD(pages);
>> + int n_pages;
>>
>> - dequeued_page = false;
>> - spin_lock_irqsave(&b_dev_info->pages_lock, flags);
>> - list_for_each_entry_safe(page, tmp, &b_dev_info->pages, lru) {
>> - /*
>> - * Block others from accessing the 'page' while we get around
>> - * establishing additional references and preparing the 'page'
>> - * to be released by the balloon driver.
>> - */
>> - if (trylock_page(page)) {
>> -#ifdef CONFIG_BALLOON_COMPACTION
>> - if (PageIsolated(page)) {
>> - /* raced with isolation */
>> - unlock_page(page);
>> - continue;
>> - }
>> -#endif
>> - balloon_page_delete(page);
>> - __count_vm_event(BALLOON_DEFLATE);
>> - unlock_page(page);
>> - dequeued_page = true;
>> - break;
>> - }
>> - }
>> - spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
>> + n_pages = balloon_page_list_dequeue(b_dev_info, &pages, 1);
>>
>> - if (!dequeued_page) {
>> + if (n_pages != 1) {
>> /*
>> * If we are unable to dequeue a balloon page because the page
>> * list is empty and there is no isolated pages, then something
>> @@ -112,9 +180,9 @@ struct page *balloon_page_dequeue(struct balloon_dev_info *b_dev_info)
>> !b_dev_info->isolated_pages))
>> BUG();
>> spin_unlock_irqrestore(&b_dev_info->pages_lock, flags);
>> - page = NULL;
>> + return NULL;
>> }
>> - return page;
>> + return list_first_entry(&pages, struct page, lru);
>> }
>> EXPORT_SYMBOL_GPL(balloon_page_dequeue);
>>
>> --
>> 2.19.1
>
>
> With above addressed:
>
> Acked-by: Michael S. Tsirkin <mst@...hat.com>
Thank you, Michael.
I addressed your feedback and I will send another version shortly.
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