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How to know shared memory between two processes?

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4

1

I need to know the amount of memory shared between two processes, that is, the intersection of their shared memories.

Any ideas?

virtual-memory shared-memory

share|improve this question

edited 30 mins ago

slm♦

266k7373 gold badges574574 silver badges720720 bronze badges

asked Nov 16 '16 at 11:49

idelvallidelvall

12311 silver badge55 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  doesn't top commands help?
  
  – Nawaz Sohail
  Nov 16 '16 at 11:50
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Which OS? Do you just want a number like "5342 kilobytes", or do you want to know which objects are shared?
  
  – Mark Plotnick
  Nov 16 '16 at 11:55
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @MarkPlotnick : I guess OP has explicitly mentioned "Amount of memory" So I don't think he is looking for "which objects are shared."
  
  – Thushi
  Nov 16 '16 at 12:04
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  ipcs -m may be the answer.
  
  – countermode
  Nov 16 '16 at 12:17
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Are you interested in just shared memory segments (shmget()), or also shared memory due to process fork & copy-on-write, mmap()ped files, etc?
  
  – Patrick
  Nov 16 '16 at 13:32
  

  
  
  
  

add a comment | 

4

1

I need to know the amount of memory shared between two processes, that is, the intersection of their shared memories.

Any ideas?

virtual-memory shared-memory

share|improve this question

edited 30 mins ago

slm♦

266k7373 gold badges574574 silver badges720720 bronze badges

asked Nov 16 '16 at 11:49

idelvallidelvall

12311 silver badge55 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  doesn't top commands help?
  
  – Nawaz Sohail
  Nov 16 '16 at 11:50
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Which OS? Do you just want a number like "5342 kilobytes", or do you want to know which objects are shared?
  
  – Mark Plotnick
  Nov 16 '16 at 11:55
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @MarkPlotnick : I guess OP has explicitly mentioned "Amount of memory" So I don't think he is looking for "which objects are shared."
  
  – Thushi
  Nov 16 '16 at 12:04
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  ipcs -m may be the answer.
  
  – countermode
  Nov 16 '16 at 12:17
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Are you interested in just shared memory segments (shmget()), or also shared memory due to process fork & copy-on-write, mmap()ped files, etc?
  
  – Patrick
  Nov 16 '16 at 13:32
  

  
  
  
  

add a comment | 

I need to know the amount of memory shared between two processes, that is, the intersection of their shared memories.

Any ideas?

virtual-memory shared-memory

share|improve this question

edited 30 mins ago

slm♦

266k7373 gold badges574574 silver badges720720 bronze badges

asked Nov 16 '16 at 11:49

idelvallidelvall

12311 silver badge55 bronze badges

share|improve this question

edited 30 mins ago

slm♦

266k7373 gold badges574574 silver badges720720 bronze badges

asked Nov 16 '16 at 11:49

idelvallidelvall

12311 silver badge55 bronze badges

share|improve this question

edited 30 mins ago

slm♦

266k7373 gold badges574574 silver badges720720 bronze badges

asked Nov 16 '16 at 11:49

idelvallidelvall

12311 silver badge55 bronze badges

edited 30 mins ago

slm♦

266k7373 gold badges574574 silver badges720720 bronze badges

edited 30 mins ago

slm♦

266k7373 gold badges574574 silver badges720720 bronze badges

asked Nov 16 '16 at 11:49

idelvallidelvall

12311 silver badge55 bronze badges

asked Nov 16 '16 at 11:49

idelvallidelvall

12311 silver badge55 bronze badges

1 Answer
1

active

oldest

votes

4

You can look at /proc/<pid>/maps, /proc/<pid>/smaps (or pmap -x <pid> if your OS supports) of interested process ID's and compare outputs to determine shared memory regions. That includes shared memory segments via shmget calls, as well as any shared libraries, files.

Edit: As mr.spuratic pointed out his answer here has more details on kernel side

You can look at a process RSS using ps, however it doesn't take into consideration all the shared pages. To see RSS for specific process, see below

cv@thunder:~$ ps -o rss,pid,comm -p $$,7023

  RSS   PID COMMAND

22060  7023 xfwm4

 6876 18094 bash

smem tool provides more detailed information, taking into consideration of shared pages. See below output for the same above process

cv@thunder:~$ smem -t |egrep "RSS|$$|7023"

  PID User     Command                         Swap      USS      PSS      RSS 

 9852 cv       grep -E RSS|18094|7023             0      340      367     2220 

18094 cv       bash                               0     3472     4043     6876 

 7023 cv       xfwm4 --display :0.0 --sm-c        0     5176     7027    22192 

From man smem:

   smem  reports  physical  memory usage, taking shared memory pages into account.  Unshared memory is reported as the USS (Unique Set Size).  Shared

   memory is divided evenly among the processes sharing that memory.  The unshared memory (USS) plus a  process's  proportion  of  shared  memory  is

   reported  as  the  PSS  (Proportional  Set  Size).   The USS and PSS only include physical memory usage.  They do not include memory that has been

   swapped out to disk.

share|improve this answer

edited Apr 13 '17 at 12:36

Community♦

1

answered Nov 16 '16 at 15:59

VenkatCVenkatC

1,57599 silver badges1010 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  thanks @VenkatC, this is insightful, but the memory addresses these files refer in their records are virtual (process space), so I can't see how they overlap. Any way of seeing how they map to physical addresses?
  
  – idelvall
  Nov 16 '16 at 17:08
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @idelvall /proc/kpageflags, see my answer to a related question here which explains some relevant kernel details.
  
  – mr.spuratic
  Nov 16 '16 at 17:21
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @idelvall you can see shared segments with 's' flag in and read more info at kernel.org/doc/Documentation/vm/pagemap.txt on converting virtual to physical.
  
  – VenkatC
  Nov 16 '16 at 18:40
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @idelvall also, what are trying exactly trying to find out or what problem are you trying to resolve?
  
  – VenkatC
  Nov 16 '16 at 18:43
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @VenkatC i want to know the total amount of RSS of a set of processes
  
  – idelvall
  Nov 16 '16 at 20:18
  

  
  
  
  

 | 
show 4 more comments

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4

You can look at /proc/<pid>/maps, /proc/<pid>/smaps (or pmap -x <pid> if your OS supports) of interested process ID's and compare outputs to determine shared memory regions. That includes shared memory segments via shmget calls, as well as any shared libraries, files.

Edit: As mr.spuratic pointed out his answer here has more details on kernel side

You can look at a process RSS using ps, however it doesn't take into consideration all the shared pages. To see RSS for specific process, see below

cv@thunder:~$ ps -o rss,pid,comm -p $$,7023

  RSS   PID COMMAND

22060  7023 xfwm4

 6876 18094 bash

smem tool provides more detailed information, taking into consideration of shared pages. See below output for the same above process

cv@thunder:~$ smem -t |egrep "RSS|$$|7023"

  PID User     Command                         Swap      USS      PSS      RSS 

 9852 cv       grep -E RSS|18094|7023             0      340      367     2220 

18094 cv       bash                               0     3472     4043     6876 

 7023 cv       xfwm4 --display :0.0 --sm-c        0     5176     7027    22192 

From man smem:

   smem  reports  physical  memory usage, taking shared memory pages into account.  Unshared memory is reported as the USS (Unique Set Size).  Shared

   memory is divided evenly among the processes sharing that memory.  The unshared memory (USS) plus a  process's  proportion  of  shared  memory  is

   reported  as  the  PSS  (Proportional  Set  Size).   The USS and PSS only include physical memory usage.  They do not include memory that has been

   swapped out to disk.

share|improve this answer

edited Apr 13 '17 at 12:36

Community♦

1

answered Nov 16 '16 at 15:59

VenkatCVenkatC

1,57599 silver badges1010 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  thanks @VenkatC, this is insightful, but the memory addresses these files refer in their records are virtual (process space), so I can't see how they overlap. Any way of seeing how they map to physical addresses?
  
  – idelvall
  Nov 16 '16 at 17:08
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @idelvall /proc/kpageflags, see my answer to a related question here which explains some relevant kernel details.
  
  – mr.spuratic
  Nov 16 '16 at 17:21
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @idelvall you can see shared segments with 's' flag in and read more info at kernel.org/doc/Documentation/vm/pagemap.txt on converting virtual to physical.
  
  – VenkatC
  Nov 16 '16 at 18:40
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @idelvall also, what are trying exactly trying to find out or what problem are you trying to resolve?
  
  – VenkatC
  Nov 16 '16 at 18:43
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @VenkatC i want to know the total amount of RSS of a set of processes
  
  – idelvall
  Nov 16 '16 at 20:18
  

  
  
  
  

 | 
show 4 more comments

4

You can look at /proc/<pid>/maps, /proc/<pid>/smaps (or pmap -x <pid> if your OS supports) of interested process ID's and compare outputs to determine shared memory regions. That includes shared memory segments via shmget calls, as well as any shared libraries, files.

Edit: As mr.spuratic pointed out his answer here has more details on kernel side

You can look at a process RSS using ps, however it doesn't take into consideration all the shared pages. To see RSS for specific process, see below

cv@thunder:~$ ps -o rss,pid,comm -p $$,7023

  RSS   PID COMMAND

22060  7023 xfwm4

 6876 18094 bash

smem tool provides more detailed information, taking into consideration of shared pages. See below output for the same above process

cv@thunder:~$ smem -t |egrep "RSS|$$|7023"

  PID User     Command                         Swap      USS      PSS      RSS 

 9852 cv       grep -E RSS|18094|7023             0      340      367     2220 

18094 cv       bash                               0     3472     4043     6876 

 7023 cv       xfwm4 --display :0.0 --sm-c        0     5176     7027    22192 

From man smem:

   smem  reports  physical  memory usage, taking shared memory pages into account.  Unshared memory is reported as the USS (Unique Set Size).  Shared

   memory is divided evenly among the processes sharing that memory.  The unshared memory (USS) plus a  process's  proportion  of  shared  memory  is

   reported  as  the  PSS  (Proportional  Set  Size).   The USS and PSS only include physical memory usage.  They do not include memory that has been

   swapped out to disk.

share|improve this answer

edited Apr 13 '17 at 12:36

Community♦

1

answered Nov 16 '16 at 15:59

VenkatCVenkatC

1,57599 silver badges1010 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  thanks @VenkatC, this is insightful, but the memory addresses these files refer in their records are virtual (process space), so I can't see how they overlap. Any way of seeing how they map to physical addresses?
  
  – idelvall
  Nov 16 '16 at 17:08
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @idelvall /proc/kpageflags, see my answer to a related question here which explains some relevant kernel details.
  
  – mr.spuratic
  Nov 16 '16 at 17:21
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @idelvall you can see shared segments with 's' flag in and read more info at kernel.org/doc/Documentation/vm/pagemap.txt on converting virtual to physical.
  
  – VenkatC
  Nov 16 '16 at 18:40
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @idelvall also, what are trying exactly trying to find out or what problem are you trying to resolve?
  
  – VenkatC
  Nov 16 '16 at 18:43
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @VenkatC i want to know the total amount of RSS of a set of processes
  
  – idelvall
  Nov 16 '16 at 20:18
  

  
  
  
  

 | 
show 4 more comments

You can look at /proc/<pid>/maps, /proc/<pid>/smaps (or pmap -x <pid> if your OS supports) of interested process ID's and compare outputs to determine shared memory regions. That includes shared memory segments via shmget calls, as well as any shared libraries, files.

Edit: As mr.spuratic pointed out his answer here has more details on kernel side

You can look at a process RSS using ps, however it doesn't take into consideration all the shared pages. To see RSS for specific process, see below

cv@thunder:~$ ps -o rss,pid,comm -p $$,7023

  RSS   PID COMMAND

22060  7023 xfwm4

 6876 18094 bash

smem tool provides more detailed information, taking into consideration of shared pages. See below output for the same above process

cv@thunder:~$ smem -t |egrep "RSS|$$|7023"

  PID User     Command                         Swap      USS      PSS      RSS 

 9852 cv       grep -E RSS|18094|7023             0      340      367     2220 

18094 cv       bash                               0     3472     4043     6876 

 7023 cv       xfwm4 --display :0.0 --sm-c        0     5176     7027    22192 

From man smem:

   smem  reports  physical  memory usage, taking shared memory pages into account.  Unshared memory is reported as the USS (Unique Set Size).  Shared

   memory is divided evenly among the processes sharing that memory.  The unshared memory (USS) plus a  process's  proportion  of  shared  memory  is

   reported  as  the  PSS  (Proportional  Set  Size).   The USS and PSS only include physical memory usage.  They do not include memory that has been

   swapped out to disk.

share|improve this answer

edited Apr 13 '17 at 12:36

Community♦

1

answered Nov 16 '16 at 15:59

VenkatCVenkatC

1,57599 silver badges1010 bronze badges

cv@thunder:~$ ps -o rss,pid,comm -p $$,7023

  RSS   PID COMMAND

22060  7023 xfwm4

 6876 18094 bash

cv@thunder:~$ smem -t |egrep "RSS|$$|7023"

  PID User     Command                         Swap      USS      PSS      RSS 

 9852 cv       grep -E RSS|18094|7023             0      340      367     2220 

18094 cv       bash                               0     3472     4043     6876 

 7023 cv       xfwm4 --display :0.0 --sm-c        0     5176     7027    22192 

   smem  reports  physical  memory usage, taking shared memory pages into account.  Unshared memory is reported as the USS (Unique Set Size).  Shared

   memory is divided evenly among the processes sharing that memory.  The unshared memory (USS) plus a  process's  proportion  of  shared  memory  is

   reported  as  the  PSS  (Proportional  Set  Size).   The USS and PSS only include physical memory usage.  They do not include memory that has been

   swapped out to disk.

share|improve this answer

edited Apr 13 '17 at 12:36

Community♦

1

answered Nov 16 '16 at 15:59

VenkatCVenkatC

1,57599 silver badges1010 bronze badges

edited Apr 13 '17 at 12:36

Community♦

1

edited Apr 13 '17 at 12:36

Community♦

1

answered Nov 16 '16 at 15:59

VenkatCVenkatC

1,57599 silver badges1010 bronze badges

answered Nov 16 '16 at 15:59

VenkatCVenkatC

1,57599 silver badges1010 bronze badges