high memory usage with malloc and file backends configured

[Bender, Charles]

Thanks so much Guillaume for clearly explaining how the file storage works. Have a good understanding of how both storage engines work so will plan accordingly.

Thanks again for your help and responding so quickly.

Charles

On Jul 10, 2017, at 2:54 PM, Guillaume Quintard <guillaume at varnish-software.com<mailto:guillaume at varnish-software.com>> wrote:

You misundestood me, but that's probably my fault :-)

The file used by the file storage will be fully allocated, ie. you;ll have a 75G file on your disk. Then varnish will mmap it to memory, which means the kernel will give Varnish a memory space corresponding to the file content. The trick is that the whole file doesn't need to be in memory, only the "active" parts are.

What happens is that we let the kernel manage that space, and it will leverage the unused memory to do so. So, true, it you had 200G of RAM, the file storage would effectively take 75G, because they would be available. That's not your case, so the kernel will only use whatever amount is unused.

That being said, outside of storage, Varnish uses roughly 1K per object stored, that's probably not impacting right now, but that's good to keep in mind.

--
Guillaume Quintard

On Mon, Jul 10, 2017 at 2:42 PM, Bender, Charles <charles at beachcamera.com<mailto:charles at beachcamera.com>> wrote:
Hi Guillaume,

Thank you for replying so quickly. I think i'm misunderstanding what file storage does. My goal is to have some objects stored in memory (malloc) and others stored on disk (file)

>From what you're saying file method still uses resident memory for each object, so with my configuration (20G malloc, 75G file) i would need 95G RAM if all storage is used? (without swap being used)

If this is the case i'm curious what the use cases are for file vs only malloc.

On Jul 10, 2017, at 1:55 PM, Guillaume Quintard <guillaume at varnish-software.com<mailto:guillaume at varnish-software.com>> wrote:

Hi Charles,

So, if I'm reading this right, there's no discrepancy. Varnish will malloc the full storage (malloc), and will mmap a file the size of the full storage (file). So even though the storage is not used, it's allocated.

Does it make sense, or did I miss something?

--
Guillaume Quintard

On Mon, Jul 10, 2017 at 1:23 PM, Bender, Charles <charles at beachcamera.com<mailto:charles at beachcamera.com>> wrote:
Hi,

There is a large discrepancy between Varnish resident memory reported by top vs reported by varnishstat. Varnish is configured with both malloc and file storage; 20G malloc and 75G file storage.

These are the startup parameters-

VARNISH_STORAGE="memcache=malloc,20G -s filecache=file,/mnt/xvdf1/varnish/varnish_storage.bin,75G"

After running for a few days top is reporting more than twice amount of memory used for varnishd process than varnishstat.

>From top-

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
 1083 varnish   20   0 82.235g 0.014t 7.765g S  75.7 51.4   2159:07 varnishd

>From varnishstat-

SMA.memcache.g_bytes                                                       5.20G        39.65K          .            5.20G         5.20G   5.20G
SMA.memcache.g_space                                                      14.80G       -39.65K          .           14.80G        14.80G              14.80G
SMF.filecache.g_bytes                                                      7.78G        27.97K          .         7.78G         7.78G         7.78G
SMF.filecache.g_space                                                     67.22G       -27.97K          .      67.22G        67.22G        67.22G

This is the relevant part of the VCL regarding storage backend selection-

sub vcl_backend_response {
                # define separate cache storage groups
                if (bereq.http.host ~ "^(encore|thereal|static)\.(beachcamera|buydig)\.com") {
                                set beresp.storage_hint = "filecache";
                                set beresp.http.X-Cache-Storage = "disk";
                } elsif (bereq.url ~ "(?i)\.(jpg|jpeg|gif|ico|pdf|swf|png|zip)") {
                                set beresp.storage_hint = "filecache";
                                set beresp.http.X-Cache-Storage = "disk";
                } elsif (bereq.url ~ "(?i)product\-image\.aspx") {
                                set beresp.storage_hint = "filecache";
                                set beresp.http.X-Cache-Storage = "disk";
                } else {
                                set beresp.storage_hint = "memcache";
                                set beresp.http.X-Cache-Storage = "memory";
                }

Can post entire VCL if needed.

Would think that since varnishstat reports 5.20G RAM used the resident memory should be around 6-7G, 14G seems excessively high. File storage should use minimal resident memory, correct?

Varnish was installed from Varnish Cache 4.1 repo. No VMODs loaded except std and directors. Using latest 4.1.7

Anything else you need please let me know.



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