linux-kernel - Re: [PATCH v2 1/2] mm/vmalloc: Use batched page requests in bulk-allocator

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Date:   Tue, 6 Jul 2021 13:26:53 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     "Uladzislau Rezki (Sony)" <urezki@...il.com>
Cc:     linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>,
        Mel Gorman <mgorman@...e.de>,
        Christoph Hellwig <hch@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Hillf Danton <hdanton@...a.com>,
        Michal Hocko <mhocko@...e.com>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH v2 1/2] mm/vmalloc: Use batched page requests in
 bulk-allocator

On Mon,  5 Jul 2021 19:05:36 +0200 "Uladzislau Rezki (Sony)" <urezki@...il.com> wrote:

> In case of simultaneous vmalloc allocations, for example it is 1GB and
> 12 CPUs my system is able to hit "BUG: soft lockup" for !CONFIG_PREEMPT
> kernel.
> 
> <snip>
> ...
>
> are obtained, i.e. do batched page requests adding cond_resched() meanwhile
> to reschedule. Batched value is hard-coded and is 100 pages per call.
> 
> Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>

Can we please have a Fixes: for this?

Is this fix important enough for 4.14-rcx?  I think so...

> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2785,10 +2785,32 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
>  	 * to fails, fallback to a single page allocator that is
>  	 * more permissive.
>  	 */
> -	if (!order)
> -		nr_allocated = alloc_pages_bulk_array_node(
> -			gfp, nid, nr_pages, pages);
> -	else
> +	if (!order) {
> +		while (nr_allocated < nr_pages) {
> +			int nr, nr_pages_request;
> +
> +			/*
> +			 * A maximum allowed request is hard-coded and is 100
> +			 * pages per call. That is done in order to prevent a
> +			 * long preemption off scenario in the bulk-allocator
> +			 * so the range is [1:100].
> +			 */
> +			nr_pages_request = min(100, (int)(nr_pages - nr_allocated));

Yes, they types are all over the place.

nr_pages: unsigned long
nr_allocated: unsigned int
nr, nr_pages_request: int

Can we please choose the most appropriate type and use that
consistently?