linux-kernel - Re: [PATCH 08/20] block, blksnap: big buffer in the form of an array of pages

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Message-ID: <YsWJgCjcS1UnBlvq@infradead.org>
Date:   Wed, 6 Jul 2022 06:09:20 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Sergei Shtepa <sergei.shtepa@...am.com>
Cc:     axboe@...nel.dk, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 08/20] block, blksnap: big buffer in the form of an array
 of pages

On Mon, Jun 13, 2022 at 06:53:01PM +0300, Sergei Shtepa wrote:
> Description of the struct big_buffer, which is used to store
> sufficiently large amounts of data, such as a CBT map, and functions for
> working with it. There are systems on which quite often the kmalloc()
> memory allocation function of several hundred kilobytes ends with an
> error code, and it is impossible to use virtual memory when handling an
> I/O unit, since a page fault situation is possible. A simple array of
> pages solves this problem.

FYI, vmalloc can now be used in a GFP_NOIO context by using
memalloc_noio_save / memalloc_noio_restore, which could be used to
simplify this a lot.