On Thu, 12 Jan 2023 15:33:48 +0000 Pasha Tatashin <pasha.tatashin@xxxxxxxxxx> wrote:
> There is 8 byte page_ext->flags field allocated per page whenever
> CONFIG_PAGE_EXTENSION is enabled. However, not every user of page_ext
> uses flags. Therefore, check whether flags is needed at least by one
> user and if so allocate space for it.
>
> For example when page_table_check is enabled, on a machine with 128G
> of memory before the fix:
>
> [ 2.244288] allocated 536870912 bytes of page_ext
> after the fix:
> [ 2.160154] allocated 268435456 bytes of page_ext
>
Looks nice.
Does it work correctly with early_page_ext=1?
> --- a/include/linux/page_ext.h
> +++ b/include/linux/page_ext.h
> @@ -12,10 +12,14 @@ struct page_ext_operations {
> size_t size;
> bool (*need)(void);
> void (*init)(void);
> + bool using_shared_ext_flags;
> };
Seems overly complicated. Can we change the three early-init
functions such as setup_early_page_ext() to simply set some global bool
flag?
> #endif
> };
>
> -unsigned long page_ext_size = sizeof(struct page_ext);
> +unsigned long page_ext_size;
>
> static unsigned long total_usage;
> static struct page_ext *lookup_page_ext(const struct page *page);
> @@ -105,6 +106,15 @@ static bool __init invoke_need_callbacks(void)
> int entries = ARRAY_SIZE(page_ext_ops);
> bool need = false;
>
> + for (i = 0; i < entries; i++) {
> + if (page_ext_ops[i]->need && page_ext_ops[i]->need()) {
I don't think this (or the below) need to check for ->need==NULL?
> + if (page_ext_ops[i]->using_shared_ext_flags) {
> + page_ext_size = sizeof(struct page_ext);
> + break;
> + }
> + }
> + }
> +
> for (i = 0; i < entries; i++) {
> if (page_ext_ops[i]->need && page_ext_ops[i]->need()) {
> page_ext_ops[i]->offset = page_ext_size;
