Commit 502d3c2a authored Mar 26, 2026 by Chenghao Duan Committed by Andrew Morton Apr 18, 2026

mm/memfd_luo: optimize shmem_recalc_inode calls in retrieve path

Move shmem_recalc_inode() out of the loop in memfd_luo_retrieve_folios()
to improve performance when restoring large memfds.

Currently, shmem_recalc_inode() is called for each folio during restore,
which is O(n) expensive operations.  This patch collects the number of
successfully added folios and calls shmem_recalc_inode() once after the
loop completes, reducing complexity to O(1).

Additionally, fix the error path to also call shmem_recalc_inode() for the
folios that were successfully added before the error occurred.

Link: https://lore.kernel.org/20260326084727.118437-3-duanchenghao@kylinos.cn


Signed-off-by: Chenghao Duan <duanchenghao@kylinos.cn>
Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: Pratyush Yadav <pratyush@kernel.org>
Cc: Haoran Jiang <jianghaoran@kylinos.cn>
Cc: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

parent ed2a29dc

mm/memfd_luo.c

+6 −2

Original line number	Diff line number	Diff line
		@@ -410,7 +410,7 @@ static int memfd_luo_retrieve_folios(struct file *file,
		struct inode *inode = file_inode(file);
		struct address_space *mapping = inode->i_mapping;
		struct folio *folio;
		long npages;
		long npages, nr_added_pages = 0;
		int err = -EIO;
		long i;

		@@ -465,12 +465,14 @@ static int memfd_luo_retrieve_folios(struct file *file,
		goto unlock_folio;
		}

		shmem_recalc_inode(inode, npages, 0);
		nr_added_pages += npages;
		folio_add_lru(folio);
		folio_unlock(folio);
		folio_put(folio);
		}

		shmem_recalc_inode(inode, nr_added_pages, 0);

		return 0;

		unlock_folio:
		@@ -489,6 +491,8 @@ static int memfd_luo_retrieve_folios(struct file *file,
		folio_put(folio);
		}

		shmem_recalc_inode(inode, nr_added_pages, 0);

		return err;
		}