On 1/15/25 03:17, Alexei Starovoitov wrote:
> From: Alexei Starovoitov <ast@xxxxxxxxxx>
>
> Introduce free_pages_nolock() that can free pages without taking locks.
> It relies on trylock and can be called from any context.
> Since spin_trylock() cannot be used in RT from hard IRQ or NMI
> it uses lockless link list to stash the pages which will be freed
> by subsequent free_pages() from good context.
>
> Do not use llist unconditionally. BPF maps continuously
> allocate/free, so we cannot unconditionally delay the freeing to
> llist. When the memory becomes free make it available to the
> kernel and BPF users right away if possible, and fallback to
> llist as the last resort.
>
> Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
With:
> @@ -4853,6 +4905,17 @@ void __free_pages(struct page *page, unsigned int order)
> }
> EXPORT_SYMBOL(__free_pages);
>
> +/*
> + * Can be called while holding raw_spin_lock or from IRQ and NMI,
> + * but only for pages that came from try_alloc_pages():
> + * order <= 3, !folio, etc
I think order > 3 is fine, as !pcp_allowed_order() case is handled too? And
what does "!folio" mean?
> + */
> +void free_pages_nolock(struct page *page, unsigned int order)
> +{
> + if (put_page_testzero(page))
> + __free_unref_page(page, order, FPI_TRYLOCK);
Hmm this will reach reset_page_owner() and thus stackdepot so same mental
note as for patch 1.
> +}
> +
> void free_pages(unsigned long addr, unsigned int order)
> {
> if (addr != 0) {
