Prevent backup reads from getting into linux page cache

Question

AFAIK all disk reads on linux get into the page cache.

Is there a way to prevent reads (done by a backup process) to get in to the page cache?

Imagine:

A server runs fine, since most operations don't need to touch the disk, since enough memory is available.
Now the backup process starts and does a lot of reading. The read bytes get into the memory (page cache) although nobody wants to read the same bytes again in the next hours.
The backup data fills up the memory and more important pages from the cache get dropped.
Server performance gets worse since more operations need to touch the disk, because the relevant pages were dropped from the cache.

My preferred solution:

Tell linux that the reads done by the backup process don't need to be stored in the page cache.

score 5 · Accepted Answer · edited Jun 20 '20 at 09:12

if you re using rsync there is the flag --drop-cache according to this question
the nocache utility which

minimize the effect an application has on the Linux file system cache

Use case: backup processes that should not interfere with the present state of the cache.

using dd there is direct I/O to bybass cache according to this question
the dd also has the option nocache option check the command info coreutils 'dd invocation'for details

Prevent backup reads from getting into linux page cache

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