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Message-ID: <29099099-7ef2-45cb-bab7-455f58de47d1@arm.com>
Date: Tue, 29 Aug 2023 15:02:22 +0100
From: Ryan Roberts <ryan.roberts@....com>
To: Matthew Wilcox <willy@...radead.org>
Cc: Will Deacon <will@...nel.org>,
"Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Nick Piggin <npiggin@...il.com>,
Peter Zijlstra <peterz@...radead.org>,
Christian Borntraeger <borntraeger@...ux.ibm.com>,
Sven Schnelle <svens@...ux.ibm.com>,
Arnd Bergmann <arnd@...db.de>,
David Hildenbrand <david@...hat.com>,
Yu Zhao <yuzhao@...gle.com>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
Yin Fengwei <fengwei.yin@...el.com>,
Yang Shi <shy828301@...il.com>,
"Huang, Ying" <ying.huang@...el.com>, Zi Yan <ziy@...dia.com>,
linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 4/4] mm/mmu_gather: Store and process pages in contig
ranges
On 25/08/2023 05:09, Matthew Wilcox wrote:
> On Thu, Aug 10, 2023 at 11:33:32AM +0100, Ryan Roberts wrote:
>> +void folios_put_refs(struct folio_range *folios, int nr)
>> +{
>> + int i;
>> + LIST_HEAD(pages_to_free);
>> + struct lruvec *lruvec = NULL;
>> + unsigned long flags = 0;
>> + unsigned int lock_batch;
>> +
>> + for (i = 0; i < nr; i++) {
>> + struct folio *folio = page_folio(folios[i].start);
>> + int refs = folios[i].end - folios[i].start;
>> +
>> + /*
>> + * Make sure the IRQ-safe lock-holding time does not get
>> + * excessive with a continuous string of pages from the
>> + * same lruvec. The lock is held only if lruvec != NULL.
>> + */
>> + if (lruvec && ++lock_batch == SWAP_CLUSTER_MAX) {
>> + unlock_page_lruvec_irqrestore(lruvec, flags);
>> + lruvec = NULL;
>> + }
>> +
>> + if (is_huge_zero_page(&folio->page))
>> + continue;
>> +
>> + if (folio_is_zone_device(folio)) {
>> + if (lruvec) {
>> + unlock_page_lruvec_irqrestore(lruvec, flags);
>> + lruvec = NULL;
>> + }
>> + if (put_devmap_managed_page(&folio->page))
>> + continue;
>> + if (folio_put_testzero(folio))
>
> We're only putting one ref for the zone_device folios? Surely
> this should be ref_sub_and_test like below?
Good point. This function is originally a copy/paste of release_pages(), and I
obviously missed this. In fact, looking at it again today, I think I'll factor
out the vast majority into a common helper, since I'm currently duplicating a
whole bunch here.
In practice I think all devmap folios will be small today though? So while I
agree I need to fix this, I think in practice it will currently do the right thing?
>
>> + free_zone_device_page(&folio->page);
>> + continue;
>> + }
>> +
>> + if (!folio_ref_sub_and_test(folio, refs))
>> + continue;
>> +
>> + if (folio_test_large(folio)) {
>> + if (lruvec) {
>> + unlock_page_lruvec_irqrestore(lruvec, flags);
>> + lruvec = NULL;
>> + }
>> + __folio_put_large(folio);
>> + continue;
>> + }
>> +
>> + if (folio_test_lru(folio)) {
>> + struct lruvec *prev_lruvec = lruvec;
>> +
>> + lruvec = folio_lruvec_relock_irqsave(folio, lruvec,
>> + &flags);
>> + if (prev_lruvec != lruvec)
>> + lock_batch = 0;
>> +
>> + lruvec_del_folio(lruvec, folio);
>> + __folio_clear_lru_flags(folio);
>> + }
>> +
>> + /*
>> + * In rare cases, when truncation or holepunching raced with
>> + * munlock after VM_LOCKED was cleared, Mlocked may still be
>> + * found set here. This does not indicate a problem, unless
>> + * "unevictable_pgs_cleared" appears worryingly large.
>> + */
>> + if (unlikely(folio_test_mlocked(folio))) {
>> + __folio_clear_mlocked(folio);
>> + zone_stat_sub_folio(folio, NR_MLOCK);
>> + count_vm_event(UNEVICTABLE_PGCLEARED);
>> + }
>
> You'll be glad to know I've factored out a nice little helper for that.
OK, what's it called? This is just copied from release_pages() at the moment.
Happy to use your helper in the refactored common helper.
>
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