The patch titled
Subject: shmem: remove check for folio lock on writepage()
has been added to the -mm mm-unstable branch. Its filename is
shmem-remove-check-for-folio-lock-on-writepage.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/shmem-remove-check-for-folio-lock-on-writepage.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@xxxxxxxxxx>
Subject: shmem: remove check for folio lock on writepage()
Date: Thu, 9 Mar 2023 15:05:40 -0800
Patch series "tmpfs: add the option to disable swap", v2.
I'm doing this work as part of future experimentation with tmpfs and the
page cache, but given a common complaint found about tmpfs is the
innability to work without the page cache I figured this might be useful
to others. It turns out it is -- at least Christian Brauner indicates
systemd uses ramfs for a few use-cases because they don't want to use swap
and so having this option would let them move over to using tmpfs for
those small use cases, see systemd-creds(1).
To see if you hit swap:
mkswap /dev/nvme2n1
swapon /dev/nvme2n1
free -h
With swap - what we see today
=============================
mount -t tmpfs -o size=5G tmpfs /data-tmpfs/
dd if=/dev/urandom of=/data-tmpfs/5g-rand2 bs=1G count=5
free -h
total used free shared buff/cache available
Mem: 3.7Gi 2.6Gi 1.2Gi 2.2Gi 2.2Gi 1.2Gi
Swap: 99Gi 2.8Gi 97Gi
Without swap
=============
free -h
total used free shared buff/cache available
Mem: 3.7Gi 387Mi 3.4Gi 2.1Mi 57Mi 3.3Gi
Swap: 99Gi 0B 99Gi
mount -t tmpfs -o size=5G -o noswap tmpfs /data-tmpfs/
dd if=/dev/urandom of=/data-tmpfs/5g-rand2 bs=1G count=5
free -h
total used free shared buff/cache available
Mem: 3.7Gi 2.6Gi 1.2Gi 2.3Gi 2.3Gi 1.1Gi
Swap: 99Gi 21Mi 99Gi
The mix and match remount testing
=================================
# Cannot disable swap after it was first enabled:
mount -t tmpfs -o size=5G tmpfs /data-tmpfs/
mount -t tmpfs -o remount -o size=5G -o noswap tmpfs /data-tmpfs/
mount: /data-tmpfs: mount point not mounted or bad option.
dmesg(1) may have more information after failed mount system call.
dmesg -c
tmpfs: Cannot disable swap on remount
# Remount with the same noswap option is OK:
mount -t tmpfs -o size=5G -o noswap tmpfs /data-tmpfs/
mount -t tmpfs -o remount -o size=5G -o noswap tmpfs /data-tmpfs/
dmesg -c
# Trying to enable swap with a remount after it first disabled:
mount -t tmpfs -o size=5G -o noswap tmpfs /data-tmpfs/
mount -t tmpfs -o remount -o size=5G tmpfs /data-tmpfs/
mount: /data-tmpfs: mount point not mounted or bad option.
dmesg(1) may have more information after failed mount system call.
dmesg -c
tmpfs: Cannot enable swap on remount if it was disabled on first mount
This patch (of 6):
Matthew notes we should not need to check the folio lock on the
writepage() callback so remove it. This sanity check has been lingering
since linux-history days. We remove this as we tidy up the writepage()
callback to make things a bit clearer.
Link: https://lkml.kernel.org/r/20230309230545.2930737-1-mcgrof@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20230309230545.2930737-2-mcgrof@xxxxxxxxxx
Signed-off-by: Luis Chamberlain <mcgrof@xxxxxxxxxx>
Suggested-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Reviewed-by: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Adam Manzanares <a.manzanares@xxxxxxxxxxx>
Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Pankaj Raghav <p.raghav@xxxxxxxxxxx>
Cc: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
---
--- a/mm/shmem.c~shmem-remove-check-for-folio-lock-on-writepage
+++ a/mm/shmem.c
@@ -1336,7 +1336,6 @@ static int shmem_writepage(struct page *
folio_clear_dirty(folio);
}
- BUG_ON(!folio_test_locked(folio));
mapping = folio->mapping;
index = folio->index;
inode = mapping->host;
_
Patches currently in -mm which might be from mcgrof@xxxxxxxxxx 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
