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mm, bpf: Introduce free_pages_nolock()

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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 PREEMPT_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.

Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/r/20250222024427.30294-4-alexei.starovoitov@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Alexei Starovoitov
2025-02-21 18:44:24 -08:00
parent 97769a53f1
commit 8c57b687e8
6 changed files with 100 additions and 14 deletions
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5
lib/stackdepot.c
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@@ -672,7 +672,10 @@ depot_stack_handle_t stack_depot_save_flags(unsigned long *entries,
exit:
if (prealloc) {
/* Stack depot didn't use this memory, free it. */
free_pages((unsigned long)prealloc, DEPOT_POOL_ORDER);
if (!allow_spin)
free_pages_nolock(virt_to_page(prealloc), DEPOT_POOL_ORDER);
else
free_pages((unsigned long)prealloc, DEPOT_POOL_ORDER);
}
if (found)
handle = found->handle.handle;