The patch titled Subject: mm: fix endless reclaim on machines with unaccepted memory has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-fix-endless-reclaim-on-machines-with-unaccepted-memory.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days

------------------------------------------------------ From: "Kirill A. Shutemov" kirill.shutemov@linux.intel.com Subject: mm: fix endless reclaim on machines with unaccepted memory Date: Fri, 9 Aug 2024 14:48:47 +0300

Unaccepted memory is considered unusable free memory, which is not counted as free on the zone watermark check. This causes get_page_from_freelist() to accept more memory to hit the high watermark, but it creates problems in the reclaim path.

The reclaim path encounters a failed zone watermark check and attempts to reclaim memory. This is usually successful, but if there is little or no reclaimable memory, it can result in endless reclaim with little to no progress. This can occur early in the boot process, just after start of the init process when the only reclaimable memory is the page cache of the init executable and its libraries.

Make unaccepted memory free from watermark check point of view. This way unaccepted memory will never be the trigger of memory reclaim. Accept more memory in the get_page_from_freelist() if needed.

Link: https://lkml.kernel.org/r/20240809114854.3745464-2-kirill.shutemov@linux.int... Signed-off-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Reported-by: Jianxiong Gao jxgao@google.com Acked-by: David Hildenbrand david@redhat.com Fixes: dcdfdd40fa82 ("mm: Add support for unaccepted memory") Cc: Borislav Petkov bp@alien8.de Cc: Johannes Weiner hannes@cmpxchg.org Cc: Kirill A. Shutemov kirill.shutemov@linux.intel.com Cc: Matthew Wilcox willy@infradead.org Cc: Mel Gorman mgorman@suse.de Cc: Mike Rapoport (Microsoft) rppt@kernel.org Cc: Tom Lendacky thomas.lendacky@amd.com Cc: Vlastimil Babka vbabka@suse.cz Cc: stable@vger.kernel.org [6.5+] Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/page_alloc.c | 42 ++++++++++++++++++++---------------------- 1 file changed, 20 insertions(+), 22 deletions(-)

--- a/mm/page_alloc.c~mm-fix-endless-reclaim-on-machines-with-unaccepted-memory +++ a/mm/page_alloc.c @@ -287,7 +287,7 @@ EXPORT_SYMBOL(nr_online_nodes);

static bool page_contains_unaccepted(struct page *page, unsigned int order); static void accept_page(struct page *page, unsigned int order); -static bool try_to_accept_memory(struct zone *zone, unsigned int order); +static bool cond_accept_memory(struct zone *zone, unsigned int order); static inline bool has_unaccepted_memory(void); static bool __free_unaccepted(struct page *page);

@@ -3072,9 +3072,6 @@ static inline long __zone_watermark_unus if (!(alloc_flags & ALLOC_CMA)) unusable_free += zone_page_state(z, NR_FREE_CMA_PAGES); #endif -#ifdef CONFIG_UNACCEPTED_MEMORY - unusable_free += zone_page_state(z, NR_UNACCEPTED); -#endif

return unusable_free; } @@ -3368,6 +3365,8 @@ retry: } }

+ cond_accept_memory(zone, order); + /* * Detect whether the number of free pages is below high * watermark. If so, we will decrease pcp->high and free @@ -3393,10 +3392,8 @@ check_alloc_wmark: gfp_mask)) { int ret;

- if (has_unaccepted_memory()) { - if (try_to_accept_memory(zone, order)) - goto try_this_zone; - } + if (cond_accept_memory(zone, order)) + goto try_this_zone;

#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT /* @@ -3450,10 +3447,8 @@ try_this_zone:

return page; } else { - if (has_unaccepted_memory()) { - if (try_to_accept_memory(zone, order)) - goto try_this_zone; - } + if (cond_accept_memory(zone, order)) + goto try_this_zone;

#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT /* Try again if zone has deferred pages */ @@ -6950,9 +6945,6 @@ static bool try_to_accept_memory_one(str struct page *page; bool last;

- if (list_empty(&zone->unaccepted_pages)) - return false; - spin_lock_irqsave(&zone->lock, flags); page = list_first_entry_or_null(&zone->unaccepted_pages, struct page, lru); @@ -6978,23 +6970,29 @@ static bool try_to_accept_memory_one(str return true; }

-static bool try_to_accept_memory(struct zone *zone, unsigned int order) +static bool cond_accept_memory(struct zone *zone, unsigned int order) { long to_accept; - int ret = false; + bool ret = false; + + if (!has_unaccepted_memory()) + return false; + + if (list_empty(&zone->unaccepted_pages)) + return false;

/* How much to accept to get to high watermark? */ to_accept = high_wmark_pages(zone) - (zone_page_state(zone, NR_FREE_PAGES) - - __zone_watermark_unusable_free(zone, order, 0)); + __zone_watermark_unusable_free(zone, order, 0) - + zone_page_state(zone, NR_UNACCEPTED));

- /* Accept at least one page */ - do { + while (to_accept > 0) { if (!try_to_accept_memory_one(zone)) break; ret = true; to_accept -= MAX_ORDER_NR_PAGES; - } while (to_accept > 0); + }

return ret; } @@ -7037,7 +7035,7 @@ static void accept_page(struct page *pag { }

-static bool try_to_accept_memory(struct zone *zone, unsigned int order) +static bool cond_accept_memory(struct zone *zone, unsigned int order) { return false; } _

Patches currently in -mm which might be from kirill.shutemov@linux.intel.com are

mm-fix-endless-reclaim-on-machines-with-unaccepted-memory.patch