linux-kernel - Re: [PATCH v3 0/4] make vmalloc gfp flags usage more apparent

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Message-ID: <20251121072945.GA30438@lst.de>
Date: Fri, 21 Nov 2025 08:29:45 +0100
From: Christoph Hellwig <hch@....de>
To: "Vishal Moola (Oracle)" <vishal.moola@...il.com>
Cc: Matthew Wilcox <willy@...radead.org>, Christoph Hellwig <hch@....de>,
	linux-xfs@...r.kernel.org, Biju Das <biju.das.jz@...renesas.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"bpf@...r.kernel.org" <bpf@...r.kernel.org>,
	"hch@...radead.org" <hch@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"urezki@...il.com" <urezki@...il.com>
Subject: Re: [PATCH v3 0/4] make vmalloc gfp flags usage more apparent

On Wed, Nov 19, 2025 at 10:55:21AM -0800, Vishal Moola (Oracle) wrote:
> > Unexpected gfp: 0x1000000 (__GFP_NOLOCKDEP). Fixing up to gfp: 0x2dc0 (GFP_KERNEL|__GFP_ZERO|__GFP_NOWARN). Fix your code!
> > 
> > I suspect __GFP_NOLOCKDEP should also be permitted by vmalloc.
> 
> As far as I can tell, theres only 1 caller of this.
> Christoph started using vmalloc for this xfs call in commit
> e2874632a621 ("xfs: use vmalloc instead of vm_map_area for buffer backing memory").
> 
> Looks like xfs uses the flag to prevent false positives. Do
> we want to continue this? If so, I'll send a patch adding the flag to
> the whitelist.

I'm not a fan of __GFP_NOLOCKDEP, but it is a valid hint for the
allocator, so it should be supported.