linux-kernel - Re: [RFC PATCH 14/39] KVM: guest_memfd: hugetlb: initialization and cleanup

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Message-ID: <Z0ykBZAOZUdf8GbB@x1n>
Date: Sun, 1 Dec 2024 12:59:33 -0500
From: Peter Xu <peterx@...hat.com>
To: Ackerley Tng <ackerleytng@...gle.com>
Cc: tabba@...gle.com, quic_eberman@...cinc.com, roypat@...zon.co.uk,
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Subject: Re: [RFC PATCH 14/39] KVM: guest_memfd: hugetlb: initialization and
 cleanup

On Tue, Sep 10, 2024 at 11:43:45PM +0000, Ackerley Tng wrote:
> +/**
> + * Removes folios in range [@lstart, @lend) from page cache of inode, updates
> + * inode metadata and hugetlb reservations.
> + */
> +static void kvm_gmem_hugetlb_truncate_folios_range(struct inode *inode,
> +						   loff_t lstart, loff_t lend)
> +{
> +	struct kvm_gmem_hugetlb *hgmem;
> +	struct hstate *h;
> +	int gbl_reserve;
> +	int num_freed;
> +
> +	hgmem = kvm_gmem_hgmem(inode);
> +	h = hgmem->h;
> +
> +	num_freed = kvm_gmem_hugetlb_filemap_remove_folios(inode->i_mapping,
> +							   h, lstart, lend);
> +
> +	gbl_reserve = hugepage_subpool_put_pages(hgmem->spool, num_freed);
> +	hugetlb_acct_memory(h, -gbl_reserve);

I wonder whether this is needed, and whether hugetlb_acct_memory() needs to
be exported in the other patch.

IIUC subpools manages the global reservation on its own when min_pages is
set (which should be gmem's case, where both max/min set to gmem size).
That's in hugepage_put_subpool() -> unlock_or_release_subpool().

> +
> +	spin_lock(&inode->i_lock);
> +	inode->i_blocks -= blocks_per_huge_page(h) * num_freed;
> +	spin_unlock(&inode->i_lock);
> +}

-- 
Peter Xu