+ shmem-move-reclaim-check-early-on-writepages.patch added to mm-unstable branch

+ shmem-move-reclaim-check-early-on-writepages.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: shmem: move reclaim check early on writepages()
has been added to the -mm mm-unstable branch.  Its filename is
     shmem-move-reclaim-check-early-on-writepages.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/shmem-move-reclaim-check-early-on-writepages.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Luis Chamberlain <mcgrof@kernel.org>
Subject: shmem: move reclaim check early on writepages()
Date: Thu, 9 Mar 2023 15:05:42 -0800

i915_gem requires huge folios to be split when swapping.  However we have
check for usage of writepages() to ensure it used only for swap purposes
later.  Avoid the splits if we're not being called for reclaim, even if
they should in theory not happen.

This makes the conditions easier to follow on shem_writepage().

Link: https://lkml.kernel.org/r/20230309230545.2930737-4-mcgrof@kernel.org
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Yosry Ahmed <yosryahmed@google.com>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Cc: Adam Manzanares <a.manzanares@samsung.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Hugh Dickins <hughd@google.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Pankaj Raghav <p.raghav@samsung.com>
---


--- a/mm/shmem.c~shmem-move-reclaim-check-early-on-writepages
+++ a/mm/shmem.c
@@ -1323,6 +1323,16 @@ static int shmem_writepage(struct page *
 	pgoff_t index;
 
 	/*
+	 * Our capabilities prevent regular writeback or sync from ever calling
+	 * shmem_writepage; but a stacking filesystem might use ->writepage of
+	 * its underlying filesystem, in which case tmpfs should write out to
+	 * swap only in response to memory pressure, and not for the writeback
+	 * threads or sync.
+	 */
+	if (WARN_ON_ONCE(!wbc->for_reclaim))
+		goto redirty;
+
+	/*
 	 * If /sys/kernel/mm/transparent_hugepage/shmem_enabled is "always" or
 	 * "force", drivers/gpu/drm/i915/gem/i915_gem_shmem.c gets huge pages,
 	 * and its shmem_writeback() needs them to be split when swapping.
@@ -1343,18 +1353,6 @@ static int shmem_writepage(struct page *
 		goto redirty;
 
 	/*
-	 * Our capabilities prevent regular writeback or sync from ever calling
-	 * shmem_writepage; but a stacking filesystem might use ->writepage of
-	 * its underlying filesystem, in which case tmpfs should write out to
-	 * swap only in response to memory pressure, and not for the writeback
-	 * threads or sync.
-	 */
-	if (!wbc->for_reclaim) {
-		WARN_ON_ONCE(1);	/* Still happens? Tell us about it! */
-		goto redirty;
-	}
-
-	/*
 	 * This is somewhat ridiculous, but without plumbing a SWAP_MAP_FALLOC
 	 * value into swapfile.c, the only way we can correctly account for a
 	 * fallocated folio arriving here is now to initialize it and write it.
_

Patches currently in -mm which might be from mcgrof@kernel.org are

shmem-remove-check-for-folio-lock-on-writepage.patch
shmem-set-shmem_writepage-variables-early.patch
shmem-move-reclaim-check-early-on-writepages.patch
shmem-skip-page-split-if-were-not-reclaiming.patch
shmem-update-documentation.patch
shmem-add-support-to-ignore-swap.patch