Hi, On 2022-11-10 14:26:20 +0700, John Naylor wrote: > On Tue, Nov 1, 2022 at 2:37 PM Thomas Munro <thomas.mu...@gmail.com> wrote: > > > Memory alignment patches: > > > > Direct I/O generally needs to be done to/from VM page-aligned > > addresses, but only "standard" 4KB pages, even when larger VM pages > > are in use (if there is an exotic system where that isn't true, it > > won't work). We need to deal with buffers on the stack, the heap and > > in shmem. For the stack, see patch 0001. For the heap and shared > > memory, see patch 0002, but David Rowley is going to propose that part > > separately, as MemoryContext API adjustments are a specialised enough > > topic to deserve another thread; here I include a copy as a > > dependency. The main direct I/O patch is 0003. > > One thing to note: Currently, a request to aset above 8kB must go into a > dedicated block. Not sure if it's a coincidence that that matches the > default PG page size, but if allocating pages on the heap is hot enough, > maybe we should consider raising that limit. Although then, aligned-to-4kB > requests would result in 16kB chunks requested unless a different allocator > was used.
With one exception, there's only a small number of places that allocate pages dynamically and we only do it for a small number of buffers. So I don't think we should worry too much about this for now. The one exception to this: GetLocalBufferStorage(). But it already batches memory allocations by increasing sizes, so I think we're good as well. Greetings, Andres Freund
