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CLOS-3583: Update physical memory limit documentation #281

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Nov 20, 2025
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CLOS-3583: Update physical memory limit documentation #281

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CLOS-3583: Update physical memory limit documentation.
nkeshelava Nov 10, 2025
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nkeshelava Nov 11, 2025
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28 changes: 28 additions & 0 deletions docs/cloudlinuxos/limits/README.md
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Expand Up @@ -234,6 +234,34 @@ In case of disk cache – if a user is starting to lack physical memory, the mem

When LVE goes over physical memory limit, CloudLinux OS will first free up memory used for disk cache, and if that is not enough, it will kill some of the processes within that LVE, and increment fPMEM counter. This will usually cause web server to serve 500 and 503 errors. Physical memory limit is a much better way to limit memory for shared hosting.

#### Physical memory lower bound

CloudLinux OS allows administrators to configure a lower bound (minimum value) for physical memory (PMEM) limits to prevent setting limits that are too low and could cause application instability. When a lower bound is configured, any attempt to set a PMEM limit below this threshold will be rejected with an error message displayed by CLI tool or CloudLinux Manager UI. This helps ensure that hosting accounts always have sufficient memory allocated for basic application requirements, preventing performance issues and unexpected application failures. The lower bound is enforced **system-wide** and applies to all limit-setting operations, whether performed through command-line tools or control panel integrations.

By default, the PMEM lower bound is not configured.

You can configure the PMEM lower bound using the <span class="notranslate">`lvectl`</span> command:

<div class="notranslate">

```
lvectl --set-pmem-lower-bound 512M
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@azheregelya azheregelya Nov 11, 2025

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lvectl

This may be too late to ask, but why did we decide to make it configurable via 2 CLI tools instead of only one? :)

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@nkeshelava nkeshelava Nov 11, 2025

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cloudlinux-limits can be used from the CLI, however it is an interface for the UI mainly. It only works with --json flag (for other options as well) and might be useful if in the future we decide to have the ability to set this lower bound from the UI. Initially I implemented it only for lvectl and Roman requested to do the same for cloudlinux-limits

```
</div>

Alternatively, you can use the <span class="notranslate">`cloudlinux-limits`</span> command:

<div class="notranslate">

```
cloudlinux-limits set --pmem-lower-bound 512M --json
```
</div>

The lower bound value accepts standard memory format notations (e.g., <span class="notranslate">`512M`</span>, <span class="notranslate">`1G`</span>, <span class="notranslate">`2048M`</span>).

The configured PMEM lower bound value is stored in the <span class="notranslate">`/etc/sysconfig/limits_lower_bounds`</span> configuration file.
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@azheregelya azheregelya Nov 11, 2025

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Makes sense to indicate what is the default value out of the box i.e. not configured.


#### Disable Page Cache accounting

Since kmod-lve 2.0-53 (for CL8) and 2.1-17 (for CL9) we have released the new sysctl param `kernel.memstat_nocache`.
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