linux-kernel - Re: [PATCH v2 4/5] mm: Refector release

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Date:   Wed, 30 Aug 2023 22:17:37 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Ryan Roberts <ryan.roberts@....com>
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 v2 4/5] mm: Refector release_pages()

On Wed, Aug 30, 2023 at 08:11:07PM +0100, Matthew Wilcox wrote:
> I'm thinking about doing ...
> 
> void release_unref_folios(struct folio_batch *folios)
> {
> 	struct lruvec *lruvec = NULL;
> 	unsigned long flags = 0;
> 	int i;
> 
> 	for (i = 0; i < folios->nr; i++) {
> 		struct folio *folio = folios->folios[i];
> 		free_swap_cache(folio);

No, can't do that here.  Swap cache has refs on the folio, so it'll
never trigger.

> 		__page_cache_release(folio, &lruvec, &flags);
> 	}
> 	mem_cgroup_uncharge_folios(folios);
> 	free_unref_folios(folios);
> }
> 
> then this becomes:
> 
> void folios_put(struct folio_batch *folios)
> {
>         int i, j;
> 
>         for (i = 0, j = 0; i < folios->nr; i++) {
>                 struct folio *folio = folios->folios[i];
> 
>                 if (is_huge_zero_page(&folio->page))
>                         continue;
>                 if (folio_is_zone_device(folio)) {
>                        if (put_devmap_managed_page(&folio->page))
>                                 continue;
>                         if (folio_put_testzero(folio))
>                                 free_zone_device_page(&folio->page);
>                         continue;
>                 }

Must go at least here, maybe earlier.

>                 if (!folio_put_testzero(folio))
>                         continue;
>                 if (folio_test_hugetlb(folio)) {
>                        free_huge_folio(folio);
>                         continue;
>                 }
> 
>                 if (j != i)
>                         folios->folios[j] = folio;
>                 j++;
>         }
> 
>         folios->nr = j;
>         if (!j)
>                 return;
> 	release_unref_folios(folios);
> }
> 
> and pfn_range_put() also becomes shorter and loses all the lruvec work.
> 
> Thoughts?
>