[PATCH] padata: use alignment when calculating the number of worker threads

[PATCH] padata: use alignment when calculating the number of worker threads

[Anthony Yznaga]

For multithreaded jobs the computed chunk size is rounded up by the
caller-specified alignment. However, the number of worker threads to
use is computed using the minimum chunk size without taking alignment
into account. A sufficiently large alignment value can result in too
many worker threads being allocated for the job.

Signed-off-by: Anthony Yznaga <anthony.yznaga@oracle.com>
---
 kernel/padata.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/padata.c b/kernel/padata.c
index e007b8a4b738..4abc536ecdb1 100644
--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -491,7 +491,7 @@ void __init padata_do_multithreaded(struct padata_mt_job *job)
 		return;
 
 	/* Ensure at least one thread when size < min_chunk. */
-	nworks = max(job->size / job->min_chunk, 1ul);
+	nworks = max(job->size / max(job->min_chunk, job->align), 1ul);
 	nworks = min(nworks, job->max_threads);
 
 	if (nworks == 1) {
-- 
1.8.3.1

Re: [PATCH] padata: use alignment when calculating the number of worker threads

[Daniel Jordan]

On Wed, Feb 22, 2023 at 04:33:12PM -0800, Anthony Yznaga wrote:
> For multithreaded jobs the computed chunk size is rounded up by the
> caller-specified alignment. However, the number of worker threads to
> use is computed using the minimum chunk size without taking alignment
> into account. A sufficiently large alignment value can result in too
> many worker threads being allocated for the job.
> 
> Signed-off-by: Anthony Yznaga <anthony.yznaga@oracle.com>

No effect for now since the page init code uses the same align and
min_chunk, but it protects future users from this problem so

Acked-by: Daniel Jordan <daniel.m.jordan@oracle.com>

Thanks.

> ---
>  kernel/padata.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/padata.c b/kernel/padata.c
> index e007b8a4b738..4abc536ecdb1 100644
> --- a/kernel/padata.c
> +++ b/kernel/padata.c
> @@ -491,7 +491,7 @@ void __init padata_do_multithreaded(struct padata_mt_job *job)
>  		return;
>  
>  	/* Ensure at least one thread when size < min_chunk. */
> -	nworks = max(job->size / job->min_chunk, 1ul);
> +	nworks = max(job->size / max(job->min_chunk, job->align), 1ul);
>  	nworks = min(nworks, job->max_threads);
>  
>  	if (nworks == 1) {
> -- 
> 1.8.3.1
> 

Re: [PATCH] padata: use alignment when calculating the number of worker threads

[Herbert Xu]

Anthony Yznaga <anthony.yznaga@oracle.com> wrote:
> For multithreaded jobs the computed chunk size is rounded up by the
> caller-specified alignment. However, the number of worker threads to
> use is computed using the minimum chunk size without taking alignment
> into account. A sufficiently large alignment value can result in too
> many worker threads being allocated for the job.
> 
> Signed-off-by: Anthony Yznaga <anthony.yznaga@oracle.com>
> ---
> kernel/padata.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)

Patch applied.  Thanks.
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt