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From: rae l on 7 May 2008 10:30
I have noticed that struct dentry_stat_t dentry_stat is a struct with
six fields,
but only 2 of them are used, other 4 have never been used since v2.6.11,

from include/linux/dcache.h:

struct dentry_stat_t {
int nr_dentry;
int nr_unused;
int age_limit; /* age in seconds */
int want_pages; /* pages requested by system */
int dummy[2];
};
extern struct dentry_stat_t dentry_stat;

(I don't know things before v2.6.11, my local linux-2.6.git repository
can only grep to v2.6.11)

$ PAGER= git grep -w -e dentry_stat
Documentation/sysctl/fs.txt:} dentry_stat = {0, 0, 45, 0,};
fs/dcache.c:struct dentry_stat_t dentry_stat = {
fs/dcache.c: * no dcache_lock, please. The caller must decrement
dentry_stat.nr_dentry
fs/dcache.c: dentry_stat.nr_unused--;
fs/dcache.c: dentry_stat.nr_dentry--; /* For d_free, below */
fs/dcache.c: dentry_stat.nr_unused++;
fs/dcache.c: dentry_stat.nr_unused--;
fs/dcache.c: dentry_stat.nr_unused++;
fs/dcache.c: dentry_stat.nr_unused++;
fs/dcache.c: dentry_stat.nr_unused--;
fs/dcache.c: dentry_stat.nr_dentry -= detached;
fs/dcache.c: dentry_stat.nr_unused++;
fs/dcache.c: return (dentry_stat.nr_unused / 100) *
sysctl_vfs_cache_pressure;
fs/dcache.c: dentry_stat.nr_dentry++;
include/linux/dcache.h:extern struct dentry_stat_t dentry_stat;
kernel/sysctl.c: .data = &dentry_stat,

it's the same as that of v2.6.11:

$ PAGER= git grep -w -e dentry_stat v2.6.11 --
v2.6.11:Documentation/sysctl/fs.txt:} dentry_stat = {0, 0, 45, 0,};
v2.6.11:fs/dcache.c:struct dentry_stat_t dentry_stat = {
v2.6.11:fs/dcache.c: * no dcache_lock, please. The caller must
decrement dentry_stat.nr_dentry
v2.6.11:fs/dcache.c: dentry_stat.nr_unused++;
v2.6.11:fs/dcache.c: dentry_stat.nr_unused--;
v2.6.11:fs/dcache.c: dentry_stat.nr_dentry--; /* For
d_free, below */
v2.6.11:fs/dcache.c: dentry_stat.nr_unused--;
v2.6.11:fs/dcache.c: dentry_stat.nr_dentry--; /* For d_free, below */
v2.6.11:fs/dcache.c: dentry_stat.nr_unused--;
v2.6.11:fs/dcache.c: dentry_stat.nr_unused++;
v2.6.11:fs/dcache.c: dentry_stat.nr_unused--;
v2.6.11:fs/dcache.c: dentry_stat.nr_unused--;
v2.6.11:fs/dcache.c: dentry_stat.nr_unused++;
v2.6.11:fs/dcache.c: dentry_stat.nr_unused--;
v2.6.11:fs/dcache.c: dentry_stat.nr_unused++;
v2.6.11:fs/dcache.c: return (dentry_stat.nr_unused / 100) *
sysctl_vfs_cache_pressure;
v2.6.11:fs/dcache.c: dentry_stat.nr_dentry++;
v2.6.11:include/linux/dcache.h:extern struct dentry_stat_t dentry_stat;
v2.6.11:kernel/sysctl.c: .data = &dentry_stat,

So I think that struct is outdated and can be simplified.

--
Cheng
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From: Matthew Wilcox on 7 May 2008 11:00
On Wed, May 07, 2008 at 10:26:58PM +0800, rae l wrote:
> I have noticed that struct dentry_stat_t dentry_stat is a struct with
> six fields,
> but only 2 of them are used, other 4 have never been used since v2.6.11,
>
> from include/linux/dcache.h:
>
> struct dentry_stat_t {
> int nr_dentry;
> int nr_unused;
> int age_limit; /* age in seconds */
> int want_pages; /* pages requested by system */
> int dummy[2];
> };

You have to not break:

$ cat /proc/sys/fs/dentry-state
122104 115846 45 0 0 0

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operating system, but compare it to ours. We can't possibly take such
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From: Ray Lee on 7 May 2008 11:10
On Wed, May 7, 2008 at 7:51 AM, Matthew Wilcox <matthew(a)wil.cx> wrote:
> On Wed, May 07, 2008 at 10:26:58PM +0800, rae l wrote:
> > I have noticed that struct dentry_stat_t dentry_stat is a struct with
> > six fields,
> > but only 2 of them are used, other 4 have never been used since v2.6.11,
> >
> > from include/linux/dcache.h:
> >
> > struct dentry_stat_t {
> > int nr_dentry;
> > int nr_unused;
> > int age_limit; /* age in seconds */
> > int want_pages; /* pages requested by system */
> > int dummy[2];
> > };
>
> You have to not break:
>
> $ cat /proc/sys/fs/dentry-state
> 122104 115846 45 0 0 0

One could hardcode the output of the last three (four?) fields, yes?
Slightly grotty, but if it comes with a decent memory savings...
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From: rae l on 7 May 2008 11:10
On Wed, May 7, 2008 at 10:51 PM, Matthew Wilcox <matthew(a)wil.cx> wrote:
> You have to not break:
>
> $ cat /proc/sys/fs/dentry-state
> 122104 115846 45 0 0 0
But why? for some applicatioins?

The struct dentry_stat can be modified to have only two useful fields,
and let the other four printed with 0,
I have greped age_limit, that's also not used anymore, why we should
let it keep 45? Or Is there some historical reason?

Or just consider /proc/sys/fs/dentry-state as a binary application interface?
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From: Matthew Wilcox on 7 May 2008 11:30
On Wed, May 07, 2008 at 08:08:09AM -0700, Ray Lee wrote:
> One could hardcode the output of the last three (four?) fields, yes?
> Slightly grotty, but if it comes with a decent memory savings...

How can it be a 'decent memory saving'? There is exactly _one_ struct
dentry_stat_t in the entire kernel. So you're talking about saving 4
ints, or 16 bytes. Bet you it'd be more bytes to hardcode printing zero.

--
Intel are signing my paycheques ... these opinions are still mine
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours. We can't possibly take such
a retrograde step."
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