Re: + drop-pagecache.patch added to -mm tree

Re: + drop-pagecache.patch added to -mm tree

[Coywolf Qi Hunt]

2005/12/2, akpm@osdl.org <akpm@osdl.org>:
>
> The patch titled
>
>      drop-pagecache
>
> has been added to the -mm tree.  Its filename is
>
>      drop-pagecache.patch
>
>
> From: Andrew Morton <akpm@osdl.org>
>
> Add /proc/sys/vm/drop-pagecache.  When written to, this will cause the kernel
> to discard as much pagecache and reclaimable slab objects as it can.
>
> It won't drop dirty data, so the user should run `sync' first.
>
> Caveats:
>
> a) Holds inode_lock for exorbitant amounts of time.
>
> b) Needs to be taught about NUMA nodes: propagate these all the way through
>    so the discarding can be controlled on a per-node basis.
>
> c) The pagecache shrinking and slab shrinking should probably have separate
>    controls.

Yes. Let /proc/sys/vm/drop-pagecache for pagecache shrinking only and
add another /proc/sys/vm/drop-slab for slab shrinking.

>
>
> Signed-off-by: Andrew Morton <akpm@osdl.org>
> ---
>
>  fs/Makefile            |    2 -
>  fs/drop-pagecache.c    |   62 +++++++++++++++++++++++++++++++++++++++++++++++++

I'd rather have drop-pagecache.c stay in mm/. Fix mm/Makefile and do
not touch fs/ at all.

-- Coywolf

>  include/linux/mm.h     |    5 +++
>  include/linux/sysctl.h |    1
>  kernel/sysctl.c        |    9 +++++++
>  mm/truncate.c          |    1
>  mm/vmscan.c            |    3 --
>  7 files changed, 79 insertions(+), 4 deletions(-)
>
> diff -puN /dev/null fs/drop-pagecache.c
> --- /dev/null   2003-09-15 06:40:47.000000000 -0700
> +++ devel-akpm/fs/drop-pagecache.c      2005-12-01 17:30:18.000000000 -0800
> @@ -0,0 +1,62 @@
> +/*
> + * Implement the manual drop-all-pagecache function
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/mm.h>
> +#include <linux/fs.h>
> +#include <linux/writeback.h>
> +#include <linux/sysctl.h>
> +#include <linux/gfp.h>
> +
> +static void drop_pagecache_sb(struct super_block *sb)
> +{
> +       struct inode *inode;
> +
> +       spin_lock(&inode_lock);
> +       list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
> +               if (inode->i_state & (I_FREEING|I_WILL_FREE))
> +                       continue;
> +               invalidate_inode_pages(inode->i_mapping);
> +       }
> +       spin_unlock(&inode_lock);
> +}
> +
> +static void drop_pagecache(void)
> +{
> +       struct super_block *sb;
> +
> +       spin_lock(&sb_lock);
> +restart:
> +       list_for_each_entry(sb, &super_blocks, s_list) {
> +               sb->s_count++;
> +               spin_unlock(&sb_lock);
> +               down_read(&sb->s_umount);
> +               if (sb->s_root)
> +                       drop_pagecache_sb(sb);
> +               up_read(&sb->s_umount);
> +               spin_lock(&sb_lock);
> +               if (__put_super_and_need_restart(sb))
> +                       goto restart;
> +       }
> +       spin_unlock(&sb_lock);
> +       printk("shrunk pagecache\n");
> +}
> +
> +static void drop_slab(void)
> +{
> +       int nr_objects;
> +
> +       do {
> +               nr_objects = shrink_slab(1000, GFP_KERNEL, 1000);
> +               printk("shrunk %d cache objects\n", nr_objects);
> +       } while (nr_objects > 10);
> +}
> +
> +int drop_pagecache_sysctl_handler(ctl_table *table, int write,
> +       struct file *file, void __user *buffer, size_t *length, loff_t *ppos)
> +{
> +       drop_pagecache();
> +       drop_slab();
> +       return 0;
> +}
> diff -puN fs/Makefile~drop-pagecache fs/Makefile
> --- devel/fs/Makefile~drop-pagecache    2005-12-01 17:30:18.000000000 -0800
> +++ devel-akpm/fs/Makefile      2005-12-01 17:30:18.000000000 -0800
> @@ -10,7 +10,7 @@ obj-y :=      open.o read_write.o file_table.
>                 ioctl.o readdir.o select.o fifo.o locks.o dcache.o inode.o \
>                 attr.o bad_inode.o file.o filesystems.o namespace.o aio.o \
>                 seq_file.o xattr.o libfs.o fs-writeback.o mpage.o direct-io.o \
> -               ioprio.o pnode.o
> +               ioprio.o pnode.o drop-pagecache.o
>
>  obj-$(CONFIG_INOTIFY)          += inotify.o
>  obj-$(CONFIG_EPOLL)            += eventpoll.o
> diff -puN include/linux/mm.h~drop-pagecache include/linux/mm.h
> --- devel/include/linux/mm.h~drop-pagecache     2005-12-01 17:30:18.000000000 -0800
> +++ devel-akpm/include/linux/mm.h       2005-12-01 17:30:18.000000000 -0800
> @@ -1078,5 +1078,10 @@ int in_gate_area_no_task(unsigned long a
>  /* /proc/<pid>/oom_adj set to -17 protects from the oom-killer */
>  #define OOM_DISABLE -17
>
> +int drop_pagecache_sysctl_handler(struct ctl_table *, int, struct file *,
> +                                       void __user *, size_t *, loff_t *);
> +int shrink_slab(unsigned long scanned, gfp_t gfp_mask,
> +                       unsigned long lru_pages);
> +
>  #endif /* __KERNEL__ */
>  #endif /* _LINUX_MM_H */
> diff -puN include/linux/sysctl.h~drop-pagecache include/linux/sysctl.h
> --- devel/include/linux/sysctl.h~drop-pagecache 2005-12-01 17:30:18.000000000 -0800
> +++ devel-akpm/include/linux/sysctl.h   2005-12-01 17:30:18.000000000 -0800
> @@ -182,6 +182,7 @@ enum
>         VM_LEGACY_VA_LAYOUT=27, /* legacy/compatibility virtual address space layout */
>         VM_SWAP_TOKEN_TIMEOUT=28, /* default time for token time out */
>         VM_SWAP_PREFETCH=29,    /* int: amount to swap prefetch */
> +       VM_DROP_PAGECACHE=30,   /* int: nuke lots of pagecache */
>  };
>
>
> diff -puN kernel/sysctl.c~drop-pagecache kernel/sysctl.c
> --- devel/kernel/sysctl.c~drop-pagecache        2005-12-01 17:30:18.000000000 -0800
> +++ devel-akpm/kernel/sysctl.c  2005-12-01 17:30:18.000000000 -0800
> @@ -783,6 +783,15 @@ static ctl_table vm_table[] = {
>                 .strategy       = &sysctl_intvec,
>         },
>         {
> +               .ctl_name       = VM_DROP_PAGECACHE,
> +               .procname       = "drop-pagecache",
> +               .data           = NULL,
> +               .maxlen         = sizeof(int),
> +               .mode           = 0644,
> +               .proc_handler   = drop_pagecache_sysctl_handler,
> +               .strategy       = &sysctl_intvec,
> +       },
> +       {
>                 .ctl_name       = VM_MIN_FREE_KBYTES,
>                 .procname       = "min_free_kbytes",
>                 .data           = &min_free_kbytes,
> diff -puN mm/truncate.c~drop-pagecache mm/truncate.c
> --- devel/mm/truncate.c~drop-pagecache  2005-12-01 17:30:18.000000000 -0800
> +++ devel-akpm/mm/truncate.c    2005-12-01 17:30:18.000000000 -0800
> @@ -256,7 +256,6 @@ unlock:
>                                 break;
>                 }
>                 pagevec_release(&pvec);
> -               cond_resched();
>         }
>         return ret;
>  }
> diff -puN mm/vmscan.c~drop-pagecache mm/vmscan.c
> --- devel/mm/vmscan.c~drop-pagecache    2005-12-01 17:30:18.000000000 -0800
> +++ devel-akpm/mm/vmscan.c      2005-12-01 17:30:18.000000000 -0800
> @@ -181,8 +181,7 @@ EXPORT_SYMBOL(remove_shrinker);
>   *
>   * Returns the number of slab objects which we shrunk.
>   */
> -static int shrink_slab(unsigned long scanned, gfp_t gfp_mask,
> -                       unsigned long lru_pages)
> +int shrink_slab(unsigned long scanned, gfp_t gfp_mask, unsigned long lru_pages)
>  {
>         struct shrinker *shrinker;
>         int ret = 0;
> _


--
Coywolf Qi Hunt

Re: + drop-pagecache.patch added to -mm tree

[Coywolf Qi Hunt]

2005/12/29, Coywolf Qi Hunt <coywolf@gmail.com>:
> 2005/12/2, akpm@osdl.org <akpm@osdl.org>:
> >
> > The patch titled
> >
> >      drop-pagecache
> >
> > has been added to the -mm tree.  Its filename is
> >
> >      drop-pagecache.patch
> >
> >
> > From: Andrew Morton <akpm@osdl.org>
> >
> > Add /proc/sys/vm/drop-pagecache.  When written to, this will cause the kernel
> > to discard as much pagecache and reclaimable slab objects as it can.
> >
> > It won't drop dirty data, so the user should run `sync' first.
> >
> > Caveats:
> >
> > a) Holds inode_lock for exorbitant amounts of time.
> >
> > b) Needs to be taught about NUMA nodes: propagate these all the way through
> >    so the discarding can be controlled on a per-node basis.
> >
> > c) The pagecache shrinking and slab shrinking should probably have separate
> >    controls.
>
> Yes. Let /proc/sys/vm/drop-pagecache for pagecache shrinking only and
> add another /proc/sys/vm/drop-slab for slab shrinking.

Hadn't checked the mm snapshort. ignore the above comment then.

>
> >
> >
> > Signed-off-by: Andrew Morton <akpm@osdl.org>
> > ---
> >
> >  fs/Makefile            |    2 -
> >  fs/drop-pagecache.c    |   62 +++++++++++++++++++++++++++++++++++++++++++++++++
>
> I'd rather have drop-pagecache.c stay in mm/. Fix mm/Makefile and do
> not touch fs/ at all.
>
> -- Coywolf
>
> >  include/linux/mm.h     |    5 +++
> >  include/linux/sysctl.h |    1
> >  kernel/sysctl.c        |    9 +++++++
> >  mm/truncate.c          |    1
> >  mm/vmscan.c            |    3 --
> >  7 files changed, 79 insertions(+), 4 deletions(-)
> >

--
Coywolf Qi Hunt

Re: + drop-pagecache.patch added to -mm tree

[Christoph Hellwig]

On Thu, Dec 29, 2005 at 05:54:08PM +0800, Coywolf Qi Hunt wrote:
> 2005/12/2, akpm@osdl.org <akpm@osdl.org>:
> >
> > The patch titled
> >
> >      drop-pagecache
> >
> > has been added to the -mm tree.  Its filename is
> >
> >      drop-pagecache.patch
> >
> >
> > From: Andrew Morton <akpm@osdl.org>
> >
> > Add /proc/sys/vm/drop-pagecache.  When written to, this will cause the kernel
> > to discard as much pagecache and reclaimable slab objects as it can.
> >
> > It won't drop dirty data, so the user should run `sync' first.
> >
> > Caveats:
> >
> > a) Holds inode_lock for exorbitant amounts of time.
> >
> > b) Needs to be taught about NUMA nodes: propagate these all the way through
> >    so the discarding can be controlled on a per-node basis.
> >
> > c) The pagecache shrinking and slab shrinking should probably have separate
> >    controls.

d) it is a total mess.

A lot of code for something that you shouldn't do
except for benchmarking.  If people see problems where pagecache data isn't
dropped enough we should fix the VM instead of adding code that just bloats
the kernel more.

Re: + drop-pagecache.patch added to -mm tree

[Andrew Morton]

Christoph Hellwig <hch@infradead.org> wrote:
>
> On Thu, Dec 29, 2005 at 05:54:08PM +0800, Coywolf Qi Hunt wrote:
> > 2005/12/2, akpm@osdl.org <akpm@osdl.org>:
> > >
> > > The patch titled
> > >
> > >      drop-pagecache
> > >
> > > has been added to the -mm tree.  Its filename is
> > >
> > >      drop-pagecache.patch
> > >
> > >
> > > From: Andrew Morton <akpm@osdl.org>
> > >
> > > Add /proc/sys/vm/drop-pagecache.  When written to, this will cause the kernel
> > > to discard as much pagecache and reclaimable slab objects as it can.
> > >
> > > It won't drop dirty data, so the user should run `sync' first.
> > >
> > > Caveats:
> > >
> > > a) Holds inode_lock for exorbitant amounts of time.
> > >
> > > b) Needs to be taught about NUMA nodes: propagate these all the way through
> > >    so the discarding can be controlled on a per-node basis.
> > >
> > > c) The pagecache shrinking and slab shrinking should probably have separate
> > >    controls.
> 
> d) it is a total mess.

Rubbish.

> A lot of code

295 bytes.

> for something that you shouldn't do
> except for benchmarking.

Sure.  It's a debugging feature.

>  If people see problems where pagecache data isn't
> dropped enough we should fix the VM instead of adding code that just bloats
> the kernel more.

It's useful for debugging VM problems, too.


I'm not fussed, really - it's useful for kernel developers and testers.  If
we're so worried about a very small amount of not-at-all-messy code then we
can stick it under CONFIG_DEBUG_VM.