linux-kernel - Re: [RFC 2/3] mm/vmalloc: add support for __GFP

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Message-ID: <YXJz4QVsNk4kUZvH@dhcp22.suse.cz>
Date:   Fri, 22 Oct 2021 10:18:41 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     NeilBrown <neilb@...e.de>
Cc:     Uladzislau Rezki <urezki@...il.com>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Dave Chinner <david@...morbit.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Hellwig <hch@...radead.org>,
        linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Ilya Dryomov <idryomov@...il.com>,
        Jeff Layton <jlayton@...nel.org>
Subject: Re: [RFC 2/3] mm/vmalloc: add support for __GFP_NOFAIL

On Fri 22-10-21 09:49:08, Neil Brown wrote:
[...]
> However now that I've thought about some more, I'd much prefer we
> introduce something like
>     memalloc_retry_wait();
> 
> and use that everywhere that a memory allocation is retried.
> I'm not convinced that we need to wait at all - at least, not when
> __GFP_DIRECT_RECLAIM is used, as in that case alloc_page will either
>   - succeed
>   - make some progress a reclaiming or
>   - sleep

There
are two that we have to do explicitly vmap_pages_range one is due to
implicit GFP_KERNEL allocations for page tables. Those would likely be a
good fit for something you suggest above. Then we have __get_vm_area_node
retry loop which can be either due to vmalloc space reservation failure
or an implicit GFP_KERNEL allocation by kasan. The first one is not
really related to the memory availability so it doesn't sound like a
good fit.

-- 
Michal Hocko
SUSE Labs