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Pagecache: use an objcache as page heap #1757

Merged
merged 4 commits into from
Aug 6, 2022
Merged

Pagecache: use an objcache as page heap #1757

merged 4 commits into from
Aug 6, 2022

Commits on Aug 6, 2022

  1. Memory management: add generic memory cleaner interface 

    With this change, it is possible to register different "memory
cleaner" closures, which will be invoked to free up memory when the
system is low on available physical memory. The virtio balloon
deflater and the pagecache drain function have been converted to
use this interface.

Partially addresses #1130.
    @francescolavra
    francescolavra committed Aug 6, 2022
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  2. objcache foreach_page_footer: refactor to allow removal from list 

    This macro is being amended so that it is possible to remove a page
list element from within the loop that walks the list. This will be
needed to implement the cache drain functionality.
    @francescolavra
    francescolavra committed Aug 6, 2022
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  3. Objcache: add locking option and drain functionality 

    This change introduces a new heap sub-type, called caching_heap,
that exports an additional callback to drain memory that has been
cached. The objcache heap is now a caching_heap.
In addition, the objcache heap now implements locking, which allows
safe use of the drain functionality in concurrently accessed heaps
without the need for an external lock.
Memory cleaner instances have been added in various places where an
objcache is used, so that caching heaps can be drained when the
system is low on memory.

Partially addresses #1494.
    @francescolavra
    francescolavra committed Aug 6, 2022
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  4. Pagecache: use an objcache as page heap 

    In the pagecache code, allocating 4KB pages directly from the
linear backed heap creates excessive fragmentation, which in
low-memory conditions may cause other allocations in the kernel
(which typically use objcaches with a 2MB page size) to fail even
when pagecache drain requests are fully executed.
This commit addresses the fragmentation issue by changing the
pagecache code to use an objcache (with a 2MB page size, and with
the linear backed heap as parent heap) as page heap; this allows a
pagecache drain to release memory in large chunks that are then
available for other allocation requests throughout the kernel.
In addition, the pagecache completion heap is now drained if a
drain request could not be fully executed by draining the page
heap.
    @francescolavra
    francescolavra committed Aug 6, 2022
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