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);

+}