Re: [PATCH 6/6] mm: Add memalloc_nowait

Michal Hocko
2020-06-25T12:40:23Z

On Thu 25-06-20 12:31:22, Matthew Wilcox wrote:
> Similar to memalloc_noio() and memalloc_nofs(), memalloc_nowait()
> guarantees we will not sleep to reclaim memory. Use it to simplify
> dm-bufio's allocations.

memalloc_nowait is a good idea! I suspect the primary usecase would be
vmalloc.

> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

[...]
> @@ -877,7 +857,9 @@ static struct dm_buffer *__alloc_buffer_wait_no_callback(struct dm_bufio_client
> */
> while (1) {
> if (dm_bufio_cache_size_latch != 1) {
> - b = alloc_buffer(c, GFP_NOWAIT | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
> + unsigned nowait_flag = memalloc_nowait_save();
> + b = alloc_buffer(c, GFP_KERNEL | __GFP_NOMEMALLOC | __GFP_NOWARN);
> + memalloc_nowait_restore(nowait_flag);

This looks confusing though. I am not familiar with alloc_buffer and
there is quite some tweaking around __GFP_NORETRY in alloc_buffer_data
which I do not follow but GFP_KERNEL just struck my eyes. So why cannot
we have
alloc_buffer(GFP_NOWAIT | __GFP_NOMEMALLOC | __GFP_NOWARN);
--
Michal Hocko
SUSE Labs