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Mon, 10 Aug 2020 12:36:03 -0700 (PDT) Date: Mon, 10 Aug 2020 12:36:03 -0700 (PDT) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Charan Teja Reddy cc: akpm@linux-foundation.org, mhocko@suse.com, vbabka@suse.cz, david@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, vinmenon@codeaurora.org Subject: Re: [PATCH] mm, page_alloc: fix core hung in free_pcppages_bulk() In-Reply-To: <1597075833-16736-1-git-send-email-charante@codeaurora.org> Message-ID: References: <1597075833-16736-1-git-send-email-charante@codeaurora.org> User-Agent: Alpine 2.23 (DEB 453 2020-06-18) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspamd-Queue-Id: 852B81004D5D9 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, 10 Aug 2020, Charan Teja Reddy wrote: > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index e4896e6..25e7e12 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3106,6 +3106,7 @@ static void free_unref_page_commit(struct page *page, unsigned long pfn) > struct zone *zone = page_zone(page); > struct per_cpu_pages *pcp; > int migratetype; > + int high; > > migratetype = get_pcppage_migratetype(page); > __count_vm_event(PGFREE); > @@ -3128,8 +3129,19 @@ static void free_unref_page_commit(struct page *page, unsigned long pfn) > pcp = &this_cpu_ptr(zone->pageset)->pcp; > list_add(&page->lru, &pcp->lists[migratetype]); > pcp->count++; > - if (pcp->count >= pcp->high) { > - unsigned long batch = READ_ONCE(pcp->batch); > + high = READ_ONCE(pcp->high); > + if (pcp->count >= high) { > + int batch; > + > + batch = READ_ONCE(pcp->batch); > + /* > + * For non-default pcp struct values, high is always > + * greater than the batch. If high < batch then pass > + * proper count to free the pcp's list pages. > + */ > + if (unlikely(high < batch)) > + batch = min(pcp->count, batch); > + > free_pcppages_bulk(zone, batch, pcp); > } > } I'm wondering if a fix to free_pcppages_bulk() is more appropriate here because the count passed into it seems otherwise fragile if this results in a hung core?