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What is a page allocation failure?
Sometimes the allocations require many physically contiguous pages which may not always be available. In times like this the kernel memory allocator may choose to fail the allocation request and this will generate a page allocation failure message to the system log.
What is page allocation in operating system?
The page allocation code. attempts to allocate a block of one or more physical pages. Pages are allocated in blocks which are powers of 2 in size. That means that it can allocate a block 1 page, 2 pages, 4 pages and so on.
What is Gfp_nowait?
If the allocation is performed from an atomic context, e.g interrupt handler, use GFP_NOWAIT . This flag prevents direct reclaim and IO or filesystem operations. Consequently, under memory pressure GFP_NOWAIT allocation is likely to fail.
What is Gfp_atomic?
GFP_ATOMIC prevents sleeping by telling the memory allocation code that it’s not allowed to sleep to satisfy the allocation – that’s all. If the memory allocation code needs to sleep, and GFP_ATOMIC has been passed, then it will return an error to the caller instead.
How does page memory allocation work?
Demand page memory allocation is the technique in which pages within a particular process or task are swapped in and out of main memory from secondary memory as required for execution. This process is also tracked through the use of page tables.
What does IMAP mean in page allocation failure?
imap: page allocation failure. order:4, mode:0xc0d0 The ‘imap:’ bit is the command that the process that had the failed allocation was running. The ‘order:4’ bit tells you how many pages were requested, but indirectly.
Why are page allocations not triggered in Linux?
The short answer is that it’s not triggered for higher order allocations, only for allocations of 32 Kb and smaller (order 3 or below). So this allocation request is just large enough to not trigger OOM processing. All things considered that’s probably a good thing.
When does the kernel start in another zone?
When the kernel is handling an allocation that started in another zone (either DMA32 or Normal on this machine), the DMA zone must have at least a certain number of pages free in order to be a fallback candidate for the allocation (sort of, it actually gets quite complicated).
How many pages does the Linux kernel request?
The kernel code always requests pages in powers of two (so one page, two contiguous pages, four contiguous pages, and so on); the ‘order’ is that power. So the order 4 request here is for 2^4 pages, which is 16 pages or 64 Kb.