linux-kernel - Re: [PATCH v3 2/2] btrfs: allocate page arrays using bulk page allocator

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Date:   Fri, 1 Apr 2022 15:26:00 +0200
From:   David Sterba <dsterba@...e.cz>
To:     Sweet Tea Dorminy <sweettea-kernel@...miny.me>
Cc:     dsterba@...e.cz, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>,
        Nick Terrell <terrelln@...com>, linux-kernel@...r.kernel.org,
        linux-btrfs@...r.kernel.org, kernel-team@...com,
        Nikolay Borisov <nborisov@...e.com>
Subject: Re: [PATCH v3 2/2] btrfs: allocate page arrays using bulk page
 allocator

On Thu, Mar 31, 2022 at 02:19:07PM -0400, Sweet Tea Dorminy wrote:
> > Also in the xfs code there's memalloc_retry_wait() which is supposed to be
> > called when repeated memory allocation is retried. What was the reason
> > you removed it?
> 
> Trying to keep the behavior as close as possible to the existing behavior.

I see, makes sense.

> The current behavior of each alloc_page loop is to fail if alloc_page() 
> fails; in the worst case, alloc_pages_bulk_array() calls alloc_page() 
> after trying to get a batch, so I figured the worst case is still 
> basically a loop calling alloc_page() and failing if it ever fails.
> 
> Reading up on it, though, arguably the memalloc_retry_wait() should 
> already be in all the callsites, so maybe I should insert a patch in the 
> middle that just adds the memalloc_retry_wait() into 
> btrfs_alloc_page_array()? Since it's an orthogonal fixup to either the 
> refactoring or the conversion to alloc_pages_bulk_array()?

Yeah a separate patch with the reasonig about the potential effects is
better. The v3 is now in misc-next with the suggested loop refactoring,
so please send the memalloc_retry_wait() update on top of that. Thanks.