What are the advantages and disadvantages if we always use mmap to allocate memory instead of malloc ?

[Siddhesh Poyarekar]

On Thu, 13 Aug 2020 at 06:50, 孙世龙 sunshilong <sunshilong369@gmail.com> wrote:
> How large are the blocks of memory?
> Will it causes a waste of memory if the entire program calls malloc to allocate
> totally 1 byte (and no such an invocation is called anymore).

One the larger side***, the allocations will be of the order of 64MB,
but there's a catch.  The allocations do not have any physical pages
backing them, so while they allocate address space, they don't
allocate any real memory except for the 1byte (or rather, ~32 bytes
(or rather, the page containing the 32 bytes), counting the alignment
requirements and malloc internal metadata) that the user requests.

Siddhesh

*** The larger side is typically for non-main arenas.  The main arena
is allocated using brk() and can be grown a page at a time.

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