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Message-ID: <5512967d-a96a-c94e-7442-e5e71baa7b19@suse.cz>
Date: Thu, 26 Nov 2020 14:45:30 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Oscar Salvador <osalvador@...e.de>, akpm@...ux-foundation.org
Cc: n-horiguchi@...jp.nec.com, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/7] mm,hwpoison: Disable pcplists before grabbing a
refcount
On 11/19/20 11:57 AM, Oscar Salvador wrote:
> Currently, we have a sort of retry mechanism to make sure pages in
> pcp-lists are spilled to the buddy system, so we can handle those.
>
> We can save us this extra checks with the new disable-pcplist mechanism
> that is available with [1].
>
> zone_pcplist_disable makes sure to 1) disable pcplists, so any page
> that is freed up from that point onwards will end up in the buddy
> system and 2) drain pcplists, so those pages that already in pcplists
> are spilled to buddy.
>
> With that, we can make a common entry point for grabbing a refcount
> from both soft_offline and memory_failure paths that is guarded by
> zone_pcplist_disable/zone_pcplist_enable.
>
> [1] https://patchwork.kernel.org/project/linux-mm/cover/20201111092812.11329-1-vbabka@suse.cz/
>
> Signed-off-by: Oscar Salvador <osalvador@...e.de>
Acked-by: Vlastimil Babka <vbabka@...e.cz>
Note as you say the series should go after [1] above, which means after
mm-page_alloc-disable-pcplists-during-memory-offline.patch in mmots, but
currently it's ordered before, where zone_pcp_disable() etc doesn't yet exist.
Found out as I review using checked out this commit from -next.
> ---
> mm/memory-failure.c | 120 +++++++++++++++++++++-----------------------
> 1 file changed, 58 insertions(+), 62 deletions(-)
>
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 4abf5d5ffc96..512613e9a1bd 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -985,26 +985,67 @@ static int __get_hwpoison_page(struct page *page)
> return 0;
> }
>
> -static int get_hwpoison_page(struct page *p)
> +/*
> + * Safely get reference count of an arbitrary page.
> + *
> + * Returns 0 for a free page, 1 for an in-use page,
> + * -EIO for a page-type we cannot handle and -EBUSY if we raced with an
> + * allocation.
> + * We only incremented refcount in case the page was already in-use and it
> + * is a known type we can handle.
> + */
> +static int get_any_page(struct page *p)
> {
> - int ret;
> - bool drained = false;
> + int ret = 0, pass = 0;
>
> -retry:
> - ret = __get_hwpoison_page(p);
> - if (!ret && !is_free_buddy_page(p) && !page_count(p) && !drained) {
> - /*
> - * The page might be in a pcplist, so try to drain those
> - * and see if we are lucky.
> - */
> - drain_all_pages(page_zone(p));
> - drained = true;
> - goto retry;
> +try_again:
> + if (!__get_hwpoison_page(p)) {
> + if (page_count(p)) {
> + /* We raced with an allocation, retry. */
> + if (pass++ < 3)
> + goto try_again;
> + ret = -EBUSY;
> + } else if (!PageHuge(p) && !is_free_buddy_page(p)) {
> + /* We raced with put_page, retry. */
> + if (pass++ < 3)
> + goto try_again;
> + ret = -EIO;
> + }
> + } else {
> + if (PageHuge(p) || PageLRU(p) || __PageMovable(p)) {
> + ret = 1;
> + } else {
> + /*
> + * A page we cannot handle. Check whether we can turn
> + * it into something we can handle.
> + */
> + if (pass++ < 3) {
> + put_page(p);
> + shake_page(p, 1);
> + goto try_again;
> + }
> + put_page(p);
> + ret = -EIO;
> + }
> }
>
> return ret;
> }
>
> +static int get_hwpoison_page(struct page *p, enum mf_flags ctxt)
> +{
> + int ret;
> +
> + zone_pcp_disable(page_zone(p));
> + if (ctxt == MF_SOFT_OFFLINE)
> + ret = get_any_page(p);
> + else
> + ret = __get_hwpoison_page(p);
> + zone_pcp_enable(page_zone(p));
> +
> + return ret;
> +}
> +
> /*
> * Do all that is necessary to remove user space mappings. Unmap
> * the pages and send SIGBUS to the processes if the data was dirty.
> @@ -1185,7 +1226,7 @@ static int memory_failure_hugetlb(unsigned long pfn, int flags)
>
> num_poisoned_pages_inc();
>
> - if (!get_hwpoison_page(p)) {
> + if (!get_hwpoison_page(p, 0)) {
> /*
> * Check "filter hit" and "race with other subpage."
> */
> @@ -1387,7 +1428,7 @@ int memory_failure(unsigned long pfn, int flags)
> * In fact it's dangerous to directly bump up page count from 0,
> * that may make page_ref_freeze()/page_ref_unfreeze() mismatch.
> */
> - if (!get_hwpoison_page(p)) {
> + if (!get_hwpoison_page(p, 0)) {
> if (is_free_buddy_page(p)) {
> if (take_page_off_buddy(p)) {
> page_ref_inc(p);
> @@ -1674,7 +1715,7 @@ int unpoison_memory(unsigned long pfn)
> return 0;
> }
>
> - if (!get_hwpoison_page(p)) {
> + if (!get_hwpoison_page(p, 0)) {
> if (TestClearPageHWPoison(p))
> num_poisoned_pages_dec();
> unpoison_pr_info("Unpoison: Software-unpoisoned free page %#lx\n",
> @@ -1705,51 +1746,6 @@ int unpoison_memory(unsigned long pfn)
> }
> EXPORT_SYMBOL(unpoison_memory);
>
> -/*
> - * Safely get reference count of an arbitrary page.
> - * Returns 0 for a free page, 1 for an in-use page, -EIO for a page-type we
> - * cannot handle and -EBUSY if we raced with an allocation.
> - * We only incremented refcount in case the page was already in-use and it is
> - * a known type we can handle.
> - */
> -static int get_any_page(struct page *p)
> -{
> - int ret = 0, pass = 0;
> -
> -try_again:
> - if (!get_hwpoison_page(p)) {
> - if (page_count(p)) {
> - /* We raced with an allocation, retry. */
> - if (pass++ < 3)
> - goto try_again;
> - ret = -EBUSY;
> - } else if (!PageHuge(p) && !is_free_buddy_page(p)) {
> - /* We raced with put_page, retry. */
> - if (pass++ < 3)
> - goto try_again;
> - ret = -EIO;
> - }
> - } else {
> - if (PageHuge(p) || PageLRU(p) || __PageMovable(p)) {
> - ret = 1;
> - } else {
> - /*
> - * A page we cannot handle. Check whether we can turn
> - * it into something we can handle.
> - */
> - if (pass++ < 3) {
> - put_page(p);
> - shake_page(p, 1);
> - goto try_again;
> - }
> - put_page(p);
> - ret = -EIO;
> - }
> - }
> -
> - return ret;
> -}
> -
> static bool isolate_page(struct page *page, struct list_head *pagelist)
> {
> bool isolated = false;
> @@ -1920,7 +1916,7 @@ int soft_offline_page(unsigned long pfn)
>
> retry:
> get_online_mems();
> - ret = get_any_page(page);
> + ret = get_hwpoison_page(page, MF_SOFT_OFFLINE);
> put_online_mems();
>
> if (ret > 0) {
>
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