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df: improve performance with many mount points

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Use hash table for seaching in filter_mount_list() and get_dev()

This improves performance for 20K mount entries from:
  real    0m1.731s
  user    0m0.532s
  sys     0m1.188s
to:
  real    0m1.066s
  user    0m0.028s
  sys     0m1.032s

* src/df.c (devlist_table): Define hash table.
(devlist_hash): Add hash function.
(devlist_compare): Add hash comparison function.
(devlist_for_dev): Add lookup function.
(devlist_free): Add cleanup function.
(filter_mount_list): Use the above hash table.
While at it, rename the variable 'devlist' to 'seen_dev' for
better readability.
(me_for_dev): Use the above lookup function.
NEWS: Mention the improvement.
THANKS.in: Remove the committer; add original submitter Josef Cejka.
This commit is contained in:
Philipp Thomas 2016-07-31 21:24:18 +02:00 committed by Pádraig Brady
parent 5bbce2d2d7
commit 1c17f61ef9
3 changed files with 81 additions and 34 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
NEWS
View File

@ -50,6 +50,9 @@ GNU coreutils NEWS -*- outline -*-
** Improvements
df now filters the system mount list more efficiently, with 20000
mount entries now being processed in about 1.1s compared to 1.7s.
install -Z now also sets the default SELinux context for created directories.
stat and tail now know about "prl_fs" (a parallels file system),

2
THANKS.in
View File

@ -321,6 +321,7 @@ Jon Peatfield J.S.Peatfield@damtp.cam.ac.uk
Joost van Baal joostvb@xs4all.nl
Jordi Pujol jordipujolp@gmail.com
Jorge Stolfi stolfi@ic.unicamp.br
Josef Cejka jcejka@suse.com
Joseph D. Wagner joe@josephdwagner.info
Joseph S. Myers jsm28@cam.ac.uk
Josh Triplett josh@freedesktop.org
@ -513,7 +514,6 @@ Petter Reinholdtsen pere@hungry.com
Phelippe Neveu pneveu@pcigeomatics.com
Phil Richards phil.richards@vf.vodafone.co.uk
Philipp Gortan gortan@gmail.com
Philipp Thomas pth@suse.de
Philippe De Muyter phdm@macqel.be
Philippe Schnoebelen Philippe.Schnoebelen@imag.fr
Phillip Jones mouse@datastacks.com

110
src/df.c
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@ -34,6 +34,7 @@
#include "mountlist.h"
#include "quote.h"
#include "find-mount-point.h"
#include "hash.h"
/* The official name of this program (e.g., no 'g' prefix). */
#define PROGRAM_NAME "df"
@ -43,14 +44,16 @@
proper_name ("David MacKenzie"), \
proper_name ("Paul Eggert")
/* Filled with device numbers of examined file systems to avoid
duplicates in output. */
static struct devlist
struct devlist
{
dev_t dev_num;
struct mount_entry *me;
struct devlist *next;
} *device_list;
};
/* Filled with device numbers of examined file systems to avoid
duplicates in output. */
static Hash_table *devlist_table;
/* If true, show even file systems with zero size or
uninteresting types. */
@ -603,23 +606,67 @@ excluded_fstype (const char *fstype)
return false;
}
static size_t
devlist_hash (void const *x, size_t table_size)
{
struct devlist const *p = x;
return (uintmax_t) p->dev_num % table_size;
}
static bool
devlist_compare (void const *x, void const *y)
{
struct devlist const *a = x;
struct devlist const *b = y;
return a->dev_num == b->dev_num;
}
static struct devlist *
devlist_for_dev (dev_t dev)
{
if (devlist_table == NULL)
return NULL;
struct devlist dev_entry;
dev_entry.dev_num = dev;
return hash_lookup (devlist_table, &dev_entry);
}
static void
devlist_free (void *p)
{
free (p);
}
/* Filter mount list by skipping duplicate entries.
In the case of duplicates - based on the device number - the mount entry
with a '/' in its me_devname (i.e., not pseudo name like tmpfs) wins.
If both have a real devname (e.g. bind mounts), then that with the shorter
me_mountdir wins. With DEVICES_ONLY == true (set with df -a), only update
the global device_list, rather than filtering the global mount_list. */
the global devlist_table, rather than filtering the global mount_list. */
static void
filter_mount_list (bool devices_only)
{
struct mount_entry *me;
/* Temporary list to keep entries ordered. */
struct devlist *device_list = NULL;
int mount_list_size = 0;
for (me = mount_list; me; me = me->me_next)
mount_list_size++;
devlist_table = hash_initialize (mount_list_size, NULL,
devlist_hash,
devlist_compare,
devlist_free);
if (devlist_table == NULL)
xalloc_die ();
/* Sort all 'wanted' entries into the list device_list. */
for (me = mount_list; me;)
{
struct stat buf;
struct devlist *devlist;
struct mount_entry *discard_me = NULL;
/* Avoid stating remote file systems as that may hang.
@ -635,21 +682,20 @@ filter_mount_list (bool devices_only)
else
{
/* If we've already seen this device... */
for (devlist = device_list; devlist; devlist = devlist->next)
if (devlist->dev_num == buf.st_dev)
break;
struct devlist *seen_dev = devlist_for_dev (buf.st_dev);
if (devlist)
if (seen_dev)
{
bool target_nearer_root = strlen (devlist->me->me_mountdir)
bool target_nearer_root = strlen (seen_dev->me->me_mountdir)
> strlen (me->me_mountdir);
/* With bind mounts, prefer items nearer the root of the source */
bool source_below_root = devlist->me->me_mntroot != NULL
bool source_below_root = seen_dev->me->me_mntroot != NULL
&& me->me_mntroot != NULL
&& (strlen (devlist->me->me_mntroot)
&& (strlen (seen_dev->me->me_mntroot)
< strlen (me->me_mntroot));
if (! print_grand_total && me->me_remote && devlist->me->me_remote
&& ! STREQ (devlist->me->me_devname, me->me_devname))
if (! print_grand_total
&& me->me_remote && seen_dev->me->me_remote
&& ! STREQ (seen_dev->me->me_devname, me->me_devname))
{
/* Don't discard remote entries with different locations,
as these are more likely to be explicitly mounted.
@ -658,21 +704,21 @@ filter_mount_list (bool devices_only)
}
else if ((strchr (me->me_devname, '/')
/* let "real" devices with '/' in the name win. */
&& ! strchr (devlist->me->me_devname, '/'))
&& ! strchr (seen_dev->me->me_devname, '/'))
/* let points towards the root of the device win. */
|| (target_nearer_root && ! source_below_root)
/* let an entry overmounted on a new device win... */
|| (! STREQ (devlist->me->me_devname, me->me_devname)
|| (! STREQ (seen_dev->me->me_devname, me->me_devname)
/* ... but only when matching an existing mnt point,
to avoid problematic replacement when given
inaccurate mount lists, seen with some chroot
environments for example. */
&& STREQ (me->me_mountdir,
devlist->me->me_mountdir)))
seen_dev->me->me_mountdir)))
{
/* Discard mount entry for existing device. */
discard_me = devlist->me;
devlist->me = me;
discard_me = seen_dev->me;
seen_dev->me = me;
}
else
{
@ -691,12 +737,14 @@ filter_mount_list (bool devices_only)
}
else
{
/* Add the device number to the global list devlist. */
devlist = xmalloc (sizeof *devlist);
/* Add the device number to the device_table. */
struct devlist *devlist = xmalloc (sizeof *devlist);
devlist->me = me;
devlist->dev_num = buf.st_dev;
devlist->next = device_list;
device_list = devlist;
if (hash_insert (devlist_table, devlist) == NULL)
xalloc_die ();
me = me->me_next;
}
@ -711,28 +759,24 @@ filter_mount_list (bool devices_only)
me = device_list->me;
me->me_next = mount_list;
mount_list = me;
/* Free devlist entry and advance. */
struct devlist *devlist = device_list->next;
free (device_list);
device_list = devlist;
device_list = device_list->next;
}
hash_free (devlist_table);
devlist_table = NULL;
}
}
/* Search a mount entry list for device id DEV.
Return the corresponding mount entry if found or NULL if not. */
static struct mount_entry const * _GL_ATTRIBUTE_PURE
me_for_dev (dev_t dev)
{
struct devlist *dl = device_list;
while (dl)
{
if (dl->dev_num == dev)
struct devlist *dl = devlist_for_dev (dev);
if (dl)
return dl->me;
dl = dl->next;
}
return NULL;
}