linux-kernel - Re: [PATCH RESEND V5,2/2] mm: shmem: implement POSIX_FADV

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Date:   Tue, 24 Jan 2023 16:01:29 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Charan Teja Kalla <quic_charante@...cinc.com>
Cc:     akpm@...ux-foundation.org, markhemm@...glemail.com,
        hughd@...gle.com, rientjes@...gle.com, surenb@...gle.com,
        shakeelb@...gle.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH RESEND V5,2/2] mm: shmem: implement
 POSIX_FADV_[WILL|DONT]NEED for shmem

On Thu, Mar 31, 2022 at 12:08:21PM +0530, Charan Teja Kalla wrote:
> +static void shmem_isolate_pages_range(struct address_space *mapping, loff_t start,
> +				loff_t end, struct list_head *list)
> +{
> +	XA_STATE(xas, &mapping->i_pages, start);
> +	struct page *page;
> +
> +	rcu_read_lock();
> +	xas_for_each(&xas, page, end) {
> +		if (xas_retry(&xas, page))
> +			continue;
> +		if (xa_is_value(page))
> +			continue;
> +
> +		if (!get_page_unless_zero(page))
> +			continue;
> +		if (isolate_lru_page(page)) {
> +			put_page(page);
> +			continue;
> +		}
> +		put_page(page);
> +
> +		if (PageUnevictable(page) || page_mapcount(page) > 1) {
> +			putback_lru_page(page);
> +			continue;
> +		}
> +
> +		/*
> +		 * Prepare the page to be passed to the reclaim_pages().
> +		 * VM couldn't reclaim the page unless we clear PG_young.
> +		 * Also, to ensure that the pages are written before
> +		 * reclaiming, page is set to dirty.
> +		 * Since we are not clearing the pte_young in the mapped
> +		 * page pte's, its reclaim may not be attempted.
> +		 */
> +		ClearPageReferenced(page);
> +		test_and_clear_page_young(page);
> +		list_add(&page->lru, list);
> +		if (need_resched()) {
> +			xas_pause(&xas);
> +			cond_resched_rcu();
> +		}
> +	}
> +	rcu_read_unlock();
> +}

This entire function needs to be converted to use folios instead of
pages if you're refreshing this patchset for current kernels.