linux-kernel - Re: [External] [PATCH v3] kexec: Enable CMA based contiguous allocation

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Message-ID: <aC2rNv49pzy1Wh3D@MiWiFi-R3L-srv>
Date: Wed, 21 May 2025 18:30:14 +0800
From: Baoquan He <bhe@...hat.com>
To: Zhongkun He <hezhongkun.hzk@...edance.com>
Cc: Alexander Graf <graf@...zon.com>, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pasha Tatashin <pasha.tatashin@...een.com>,
	nh-open-source@...zon.com
Subject: Re: [External] [PATCH v3] kexec: Enable CMA based contiguous
 allocation

On 05/21/25 at 03:47pm, Zhongkun He wrote:
> On Wed, May 14, 2025 at 2:40 AM Alexander Graf <graf@...zon.com> wrote:
......
> >  /**
> >   * kexec_locate_mem_hole - find free memory for the purgatory or the next kernel
> >   * @kbuf:      Parameters for the memory search.
> > @@ -648,6 +684,13 @@ int kexec_locate_mem_hole(struct kexec_buf *kbuf)
> >         if (kbuf->mem != KEXEC_BUF_MEM_UNKNOWN)
> >                 return 0;
> >
> > +       /*
> > +        * Try to find a free physically contiguous block of memory first. With that, we
> > +        * can avoid any copying at kexec time.
> > +        */
> > +       if (!kexec_alloc_contig(kbuf))
> > +               return 0;
> 
> IIUC, The kexec_locate_mem_hole() function is also used in
> the KEXEC_TYPE_CRASH kimage, but kexec_alloc_contig() does not skip it.
> This can cause kdump to fail and lead to CMA memory leakage.

That is true and good catch, and fix is needed to skip cma alloc for
kdump.

> 
> So I ran some tests, as listed below:
> The CMA memory decreases with each execution of the kdump-config
> reload operation.
> 
> /home/hezhongkun.hzk# kdump-config reload
> unloaded kdump kernel.
> Creating symlink /var/lib/kdump/vmlinuz.
> Creating symlink /var/lib/kdump/initrd.img.
> kexec_file_load failed: Cannot assign requested address
> failed to load kdump kernel ... failed!
> 
> [ 1387.536346] kexec_file: allocated 1817 DMA pages at 0x11b16e
> [ 1399.147677] kexec_file: allocated 113 DMA pages at 0x119087
> [ 1399.148915] kexec_file: allocated 5 DMA pages at 0x1140f8
> [ 1399.150266] kexec_file: allocated 2 DMA pages at 0x1118fd
> [ 1399.151474] kexec_file: allocated 8302 DMA pages at 0x11b900
> 
> /home/hezhongkun.hzk# cat /proc/meminfo | grep Cma
> CmaTotal:        1048576 kB
> CmaFree:          679972 kB
> /home/hezhongkun.hzk# cat /proc/meminfo | grep Cma
> CmaTotal:        1048576 kB
> CmaFree:          639016 kB
> /home/hezhongkun.hzk# cat /proc/meminfo | grep Cma
> CmaTotal:        1048576 kB
> CmaFree:          557104 kB
> 
> cat /proc/meminfo | grep Cma
> CmaTotal:        1048576 kB
> CmaFree:          557104 kB
> 
> > +
> >         if (!IS_ENABLED(CONFIG_ARCH_KEEP_MEMBLOCK))
> >                 ret = kexec_walk_resources(kbuf, locate_mem_hole_callback);
> >         else
> > @@ -693,6 +736,7 @@ int kexec_add_buffer(struct kexec_buf *kbuf)
> >         /* Ensure minimum alignment needed for segments. */
> >         kbuf->memsz = ALIGN(kbuf->memsz, PAGE_SIZE);
> >         kbuf->buf_align = max(kbuf->buf_align, PAGE_SIZE);
> > +       kbuf->cma = NULL;
> >
> >         /* Walk the RAM ranges and allocate a suitable range for the buffer */
> >         ret = arch_kexec_locate_mem_hole(kbuf);
> > @@ -705,6 +749,7 @@ int kexec_add_buffer(struct kexec_buf *kbuf)
> >         ksegment->bufsz = kbuf->bufsz;
> >         ksegment->mem = kbuf->mem;
> >         ksegment->memsz = kbuf->memsz;
> > +       kbuf->image->segment_cma[kbuf->image->nr_segments] = kbuf->cma;
> >         kbuf->image->nr_segments++;
> >         return 0;
> >  }
> > diff --git a/kernel/kexec_internal.h b/kernel/kexec_internal.h
> > index d35d9792402d..29e6cebe0c43 100644
> > --- a/kernel/kexec_internal.h
> > +++ b/kernel/kexec_internal.h
> > @@ -10,7 +10,7 @@ struct kimage *do_kimage_alloc_init(void);
> >  int sanity_check_segment_list(struct kimage *image);
> >  void kimage_free_page_list(struct list_head *list);
> >  void kimage_free(struct kimage *image);
> > -int kimage_load_segment(struct kimage *image, struct kexec_segment *segment);
> > +int kimage_load_segment(struct kimage *image, int idx);
> >  void kimage_terminate(struct kimage *image);
> >  int kimage_is_destination_range(struct kimage *image,
> >                                 unsigned long start, unsigned long end);
> > --
> > 2.34.1
> >
> >
> >
> >
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> >
>