linux-kernel - Re: [PATCH v1 0/2] mm: cma: introduce a non-blocking version of cma

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Message-ID: <F8551A10-E254-44FC-B28E-9E7F8AC14B57@nvidia.com>
Date:   Thu, 22 Oct 2020 19:42:45 -0400
From:   Zi Yan <ziy@...dia.com>
To:     Roman Gushchin <guro@...com>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        <saberlily.xia@...ilicon.com>, <linux-kernel@...r.kernel.org>,
        <linux-mm@...ck.org>, <kernel-team@...com>
Subject: Re: [PATCH v1 0/2] mm: cma: introduce a non-blocking version of
 cma_release()

On 22 Oct 2020, at 18:53, Roman Gushchin wrote:

> This small patchset introduces a non-blocking version of cma_release()
> and simplifies the code in hugetlbfs, where previously we had to
> temporarily drop hugetlb_lock around the cma_release() call.
>
> It should help Zi Yan on his work on 1 GB THPs: splitting a gigantic
> THP under a memory pressure requires a cma_release() call. If it's

Thanks for the patch. But during 1GB THP split, we only clear
the bitmaps without releasing the pages. Also in cma_release_nowait(),
the first page in the allocated CMA region is reused to store
struct cma_clear_bitmap_work, but the same method cannot be used
during THP split, since the first page is still in-use. We might
need to allocate some new memory for struct cma_clear_bitmap_work,
which might not be successful under memory pressure. Any suggestion
on where to store struct cma_clear_bitmap_work when I only want to
clear bitmap without releasing the pages?

Thanks.

—
Best Regards,
Yan Zi

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