* [PATCH] fs: drop_caches: skip dropping pagecache which is always dirty
@ 2022-07-20 2:21 cgel.zte
2022-07-20 3:02 ` Matthew Wilcox
0 siblings, 1 reply; 7+ messages in thread
From: cgel.zte @ 2022-07-20 2:21 UTC (permalink / raw)
To: viro, hughd, akpm, hch, hsiangkao
Cc: yang.yang29, axboe, yangerkun, johannes.thumshirn, linux-fsdevel,
linux-kernel, linux-mm, Ran Xiaokai, CGEL ZTE
From: Yang Yang <yang.yang29@zte.com.cn>
Pagecache of some kind of fs has PG_dirty bit set once it was
allocated, so it can't be dropped. These fs include ramfs and
tmpfs. This can make drop_pagecache_sb() more efficient.
Introduce a new fs flag to do this, and this new flag may be
used in other case in future.
Signed-off-by: Ran Xiaokai <ran.xiaokai@zte.com.cn>
Signed-off-by: Yang Yang <yang.yang29@zte.com.cn>
Signed-off-by: CGEL ZTE <cgel.zte@gmail.com>
---
fs/drop_caches.c | 7 +++++++
fs/ramfs/inode.c | 2 +-
include/linux/fs.h | 1 +
mm/shmem.c | 2 +-
4 files changed, 10 insertions(+), 2 deletions(-)
diff --git a/fs/drop_caches.c b/fs/drop_caches.c
index e619c31b6bd9..16956d5d3922 100644
--- a/fs/drop_caches.c
+++ b/fs/drop_caches.c
@@ -19,6 +19,13 @@ static void drop_pagecache_sb(struct super_block *sb, void *unused)
{
struct inode *inode, *toput_inode = NULL;
+ /*
+ * Pagecache of this kind of fs has PG_dirty bit set once it was
+ * allocated, so it can't be dropped.
+ */
+ if (sb->s_type->fs_flags & FS_ALWAYS_DIRTY)
+ return;
+
spin_lock(&sb->s_inode_list_lock);
list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
spin_lock(&inode->i_lock);
diff --git a/fs/ramfs/inode.c b/fs/ramfs/inode.c
index bc66d0173e33..5fb62d37618f 100644
--- a/fs/ramfs/inode.c
+++ b/fs/ramfs/inode.c
@@ -289,7 +289,7 @@ static struct file_system_type ramfs_fs_type = {
.init_fs_context = ramfs_init_fs_context,
.parameters = ramfs_fs_parameters,
.kill_sb = ramfs_kill_sb,
- .fs_flags = FS_USERNS_MOUNT,
+ .fs_flags = FS_USERNS_MOUNT | FS_ALWAYS_DIRTY,
};
static int __init init_ramfs_fs(void)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index e285bd9d6188..90cdd10d683e 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2532,6 +2532,7 @@ struct file_system_type {
#define FS_USERNS_MOUNT 8 /* Can be mounted by userns root */
#define FS_DISALLOW_NOTIFY_PERM 16 /* Disable fanotify permission events */
#define FS_ALLOW_IDMAP 32 /* FS has been updated to handle vfs idmappings. */
+#define FS_ALWAYS_DIRTY 64 /* Pagecache is always dirty. */
#define FS_RENAME_DOES_D_MOVE 32768 /* FS will handle d_move() during rename() internally. */
int (*init_fs_context)(struct fs_context *);
const struct fs_parameter_spec *parameters;
diff --git a/mm/shmem.c b/mm/shmem.c
index 8baf26eda989..5d549f61735f 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -3974,7 +3974,7 @@ static struct file_system_type shmem_fs_type = {
.parameters = shmem_fs_parameters,
#endif
.kill_sb = kill_litter_super,
- .fs_flags = FS_USERNS_MOUNT,
+ .fs_flags = FS_USERNS_MOUNT | FS_ALWAYS_DIRTY,
};
void __init shmem_init(void)
--
2.25.1
^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH] fs: drop_caches: skip dropping pagecache which is always dirty
2022-07-20 2:21 [PATCH] fs: drop_caches: skip dropping pagecache which is always dirty cgel.zte
@ 2022-07-20 3:02 ` Matthew Wilcox
2022-07-20 6:02 ` CGEL
0 siblings, 1 reply; 7+ messages in thread
From: Matthew Wilcox @ 2022-07-20 3:02 UTC (permalink / raw)
To: cgel.zte
Cc: viro, hughd, akpm, hch, hsiangkao, yang.yang29, axboe, yangerkun,
johannes.thumshirn, linux-fsdevel, linux-kernel, linux-mm,
Ran Xiaokai
On Wed, Jul 20, 2022 at 02:21:19AM +0000, cgel.zte@gmail.com wrote:
> From: Yang Yang <yang.yang29@zte.com.cn>
>
> Pagecache of some kind of fs has PG_dirty bit set once it was
> allocated, so it can't be dropped. These fs include ramfs and
> tmpfs. This can make drop_pagecache_sb() more efficient.
Why do we want to make drop_pagecache_sb() more efficient?
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] fs: drop_caches: skip dropping pagecache which is always dirty
2022-07-20 3:02 ` Matthew Wilcox
@ 2022-07-20 6:02 ` CGEL
2022-07-20 6:04 ` Christoph Hellwig
2022-07-20 15:02 ` Matthew Wilcox
0 siblings, 2 replies; 7+ messages in thread
From: CGEL @ 2022-07-20 6:02 UTC (permalink / raw)
To: Matthew Wilcox
Cc: viro, hughd, akpm, hch, hsiangkao, yang.yang29, axboe, yangerkun,
johannes.thumshirn, linux-fsdevel, linux-kernel, linux-mm,
Ran Xiaokai
On Wed, Jul 20, 2022 at 04:02:40AM +0100, Matthew Wilcox wrote:
> On Wed, Jul 20, 2022 at 02:21:19AM +0000, cgel.zte@gmail.com wrote:
> > From: Yang Yang <yang.yang29@zte.com.cn>
> >
> > Pagecache of some kind of fs has PG_dirty bit set once it was
> > allocated, so it can't be dropped. These fs include ramfs and
> > tmpfs. This can make drop_pagecache_sb() more efficient.
>
> Why do we want to make drop_pagecache_sb() more efficient?
Some users may use drop_caches besides testing or debugging.
For example, some systems will create a lot of pagecache when boot up
while reading bzImage, ramdisk, docker images etc. Most of this pagecache
is useless after boot up. It may has a longterm negative effects for the
workload when trigger page reclaim. It is especially harmful when trigger
direct_reclaim or we need allocate pages in atomic context. So users may
chose to drop_caches after boot up.
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] fs: drop_caches: skip dropping pagecache which is always dirty
2022-07-20 6:02 ` CGEL
@ 2022-07-20 6:04 ` Christoph Hellwig
2022-07-20 7:01 ` CGEL
2022-07-20 15:02 ` Matthew Wilcox
1 sibling, 1 reply; 7+ messages in thread
From: Christoph Hellwig @ 2022-07-20 6:04 UTC (permalink / raw)
To: CGEL
Cc: Matthew Wilcox, viro, hughd, akpm, hch, hsiangkao, yang.yang29,
axboe, yangerkun, johannes.thumshirn, linux-fsdevel,
linux-kernel, linux-mm, Ran Xiaokai
On Wed, Jul 20, 2022 at 06:02:32AM +0000, CGEL wrote:
> For example, some systems will create a lot of pagecache when boot up
> while reading bzImage, ramdisk, docker images etc. Most of this pagecache
> is useless after boot up. It may has a longterm negative effects for the
> workload when trigger page reclaim. It is especially harmful when trigger
> direct_reclaim or we need allocate pages in atomic context. So users may
> chose to drop_caches after boot up.
It is purely a debug interface. If you want to drop specific page cache
that needs to be done through madvise.
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] fs: drop_caches: skip dropping pagecache which is always dirty
2022-07-20 6:04 ` Christoph Hellwig
@ 2022-07-20 7:01 ` CGEL
0 siblings, 0 replies; 7+ messages in thread
From: CGEL @ 2022-07-20 7:01 UTC (permalink / raw)
To: Christoph Hellwig
Cc: Matthew Wilcox, viro, hughd, akpm, hsiangkao, yang.yang29, axboe,
yangerkun, johannes.thumshirn, linux-fsdevel, linux-kernel,
linux-mm, Ran Xiaokai
On Tue, Jul 19, 2022 at 11:04:36PM -0700, Christoph Hellwig wrote:
> On Wed, Jul 20, 2022 at 06:02:32AM +0000, CGEL wrote:
> > For example, some systems will create a lot of pagecache when boot up
> > while reading bzImage, ramdisk, docker images etc. Most of this pagecache
> > is useless after boot up. It may has a longterm negative effects for the
> > workload when trigger page reclaim. It is especially harmful when trigger
> > direct_reclaim or we need allocate pages in atomic context. So users may
> > chose to drop_caches after boot up.
>
> It is purely a debug interface. If you want to drop specific page cache
> that needs to be done through madvise.
It's not easy for users to use madvise in complex system, it takes cost.
Since drop_caches is not forbidden, and users may want simply use it in
the scene above mail described.
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] fs: drop_caches: skip dropping pagecache which is always dirty
2022-07-20 6:02 ` CGEL
2022-07-20 6:04 ` Christoph Hellwig
@ 2022-07-20 15:02 ` Matthew Wilcox
2022-07-21 1:00 ` CGEL
1 sibling, 1 reply; 7+ messages in thread
From: Matthew Wilcox @ 2022-07-20 15:02 UTC (permalink / raw)
To: CGEL
Cc: viro, hughd, akpm, hch, hsiangkao, yang.yang29, axboe, yangerkun,
johannes.thumshirn, linux-fsdevel, linux-kernel, linux-mm,
Ran Xiaokai
On Wed, Jul 20, 2022 at 06:02:32AM +0000, CGEL wrote:
> On Wed, Jul 20, 2022 at 04:02:40AM +0100, Matthew Wilcox wrote:
> > On Wed, Jul 20, 2022 at 02:21:19AM +0000, cgel.zte@gmail.com wrote:
> > > From: Yang Yang <yang.yang29@zte.com.cn>
> > >
> > > Pagecache of some kind of fs has PG_dirty bit set once it was
> > > allocated, so it can't be dropped. These fs include ramfs and
> > > tmpfs. This can make drop_pagecache_sb() more efficient.
> >
> > Why do we want to make drop_pagecache_sb() more efficient?
>
> Some users may use drop_caches besides testing or debugging.
This is a terrible reason.
> For example, some systems will create a lot of pagecache when boot up
> while reading bzImage, ramdisk, docker images etc. Most of this pagecache
> is useless after boot up. It may has a longterm negative effects for the
> workload when trigger page reclaim. It is especially harmful when trigger
> direct_reclaim or we need allocate pages in atomic context. So users may
> chose to drop_caches after boot up.
If that's actually a problem, work on fixing that.
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH] fs: drop_caches: skip dropping pagecache which is always dirty
2022-07-20 15:02 ` Matthew Wilcox
@ 2022-07-21 1:00 ` CGEL
0 siblings, 0 replies; 7+ messages in thread
From: CGEL @ 2022-07-21 1:00 UTC (permalink / raw)
To: Matthew Wilcox
Cc: viro, hughd, akpm, hch, hsiangkao, yang.yang29, axboe, yangerkun,
johannes.thumshirn, linux-fsdevel, linux-kernel, linux-mm,
Ran Xiaokai
On Wed, Jul 20, 2022 at 04:02:04PM +0100, Matthew Wilcox wrote:
> On Wed, Jul 20, 2022 at 06:02:32AM +0000, CGEL wrote:
> > On Wed, Jul 20, 2022 at 04:02:40AM +0100, Matthew Wilcox wrote:
> > > On Wed, Jul 20, 2022 at 02:21:19AM +0000, cgel.zte@gmail.com wrote:
> > > > From: Yang Yang <yang.yang29@zte.com.cn>
> > > >
> > > > Pagecache of some kind of fs has PG_dirty bit set once it was
> > > > allocated, so it can't be dropped. These fs include ramfs and
> > > > tmpfs. This can make drop_pagecache_sb() more efficient.
> > >
> > > Why do we want to make drop_pagecache_sb() more efficient?
> >
> > Some users may use drop_caches besides testing or debugging.
>
> This is a terrible reason.
>
Another case that may use drop_caches: "Migration of virtual machines
will go faster if there are fewer pages to copy, so administrators would
like to be able to force a virtual machine to reclaim as much memory as
possible before the migration begins. "
See https://lwn.net/Articles/894849/
> > For example, some systems will create a lot of pagecache when boot up
> > while reading bzImage, ramdisk, docker images etc. Most of this pagecache
> > is useless after boot up. It may has a longterm negative effects for the
> > workload when trigger page reclaim. It is especially harmful when trigger
> > direct_reclaim or we need allocate pages in atomic context. So users may
> > chose to drop_caches after boot up.
>
> If that's actually a problem, work on fixing that.
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2022-07-21 1:00 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-07-20 2:21 [PATCH] fs: drop_caches: skip dropping pagecache which is always dirty cgel.zte
2022-07-20 3:02 ` Matthew Wilcox
2022-07-20 6:02 ` CGEL
2022-07-20 6:04 ` Christoph Hellwig
2022-07-20 7:01 ` CGEL
2022-07-20 15:02 ` Matthew Wilcox
2022-07-21 1:00 ` CGEL
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