linux-kernel - Re: [PATCH v5 02/11] mm/mempolicy: introduce MPOL_WEIGHTED

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Date: Fri, 5 Jan 2024 02:25:28 -0500
From: Gregory Price <gregory.price@...verge.com>
To: "Huang, Ying" <ying.huang@...el.com>
Cc: Gregory Price <gourry.memverge@...il.com>, linux-mm@...ck.org,
	linux-doc@...r.kernel.org, linux-fsdevel@...r.kernel.org,
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	sthanneeru@...ron.com, emirakhur@...ron.com, Hasan.Maruf@....com,
	seungjun.ha@...sung.com,
	Srinivasulu Thanneeru <sthanneeru.opensrc@...ron.com>
Subject: Re: [PATCH v5 02/11] mm/mempolicy: introduce
 MPOL_WEIGHTED_INTERLEAVE for weighted interleaving

On Fri, Jan 05, 2024 at 02:51:40PM +0800, Huang, Ying wrote:
> >
> > So we're talking ~1MB for 1024 threads with mempolicies to avoid error
> > conditions mid-page-allocation and to reduce the cost associated with
> > applying weighted interleave.
> 
> Think about this again.  Why do we need weights array on stack?  I think
> this is used to keep weights consistent.  If so, we don't need weights
> array on stack.  Just use RCU to access global weights array.
> 

>From the bulk allocation code:

__alloc_pages_bulk(gfp, node, NULL, node_pages, NULL, page_array);

This function can block. You cannot block during an RCU read context.

~Gregory