56e0be34bc
In commit b6923420f3 (MDEV-29445)
we started to specify the MAP_POPULATE flag for allocating the
InnoDB buffer pool. This would cause a lot of time to be spent
on __mm_populate() inside the Linux kernel, such as 16 seconds
to pre-fault or commit innodb_buffer_pool_size=64G.
Let us revert to the previous way of allocating the buffer pool
at startup. Note: An attempt to increase the buffer pool size by
SET GLOBAL innodb_buffer_pool_size (up to innodb_buffer_pool_size_max)
will invoke my_virtual_mem_commit(), which will use MAP_POPULATE
to zero-fill and prefault the requested additional memory area, blocking
buf_pool.mutex.
Before MDEV-29445 we allocated the InnoDB buffer pool by invoking
mmap(2) once (via my_large_malloc()). After the change, we would
invoke mmap(2) twice, first via my_virtual_mem_reserve() and then
via my_virtual_mem_commit(). Outside Microsoft Windows, we are
reverting back to my_large_malloc() like allocation.
my_virtual_mem_reserve(): Define only for Microsoft Windows.
Other platforms should invoke my_large_virtual_alloc() and
update_malloc_size() instead of my_virtual_mem_reserve() and
my_virtual_mem_commit().
my_large_virtual_alloc(): Define only outside Microsoft Windows.
Do not specify MAP_NORESERVE nor MAP_POPULATE, to preserve compatibility
with my_large_malloc(). Were MAP_POPULATE specified, the mmap()
system call would be significantly slower, for example 18 seconds
to reserve 64 GiB upfront.
Code status:
ci.appveyor.com
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