Re: [PATCH v2] alloc_tag: handle incomplete bulk allocations in vm_module_tags_populate

[Suren Baghdasaryan]

On Wed, Apr 9, 2025 at 7:52 PM Yunsheng Lin <linyunsheng@xxxxxxxxxx> wrote:
>
> On 2025/4/10 9:44, Suren Baghdasaryan wrote:
> > On Thu, Apr 10, 2025 at 12:12 AM Andrew Morton
> > <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> >>
> >> On Wed,  9 Apr 2025 22:51:11 +0000 "T.J. Mercier" <tjmercier@xxxxxxxxxx> wrote:
> >>
> >>> alloc_pages_bulk_node may partially succeed and allocate fewer than the
> >>> requested nr_pages. There are several conditions under which this can
> >>> occur, but we have encountered the case where CONFIG_PAGE_OWNER is
> >>> enabled causing all bulk allocations to always fallback to single page
> >>> allocations due to commit 187ad460b841 ("mm/page_alloc: avoid page
> >>> allocator recursion with pagesets.lock held").
> >>>
> >>> Currently vm_module_tags_populate immediately fails when
> >>> alloc_pages_bulk_node returns fewer than the requested number of pages.
> >>> When this happens memory allocation profiling gets disabled, for example
> >>>
> >>> [   14.297583] [9:       modprobe:  465] Failed to allocate memory for allocation tags in the module scsc_wlan. Memory allocation profiling is disabled!
> >>> [   14.299339] [9:       modprobe:  465] modprobe: Failed to insmod '/vendor/lib/modules/scsc_wlan.ko' with args '': Out of memory
> >>>
> >>> This patch causes vm_module_tags_populate to retry bulk allocations for
> >>> the remaining memory instead of failing immediately which will avoid the
> >>> disablement of memory allocation profiling.
> >>>
> >>
> >> Thanks.  I'm assuming we want cc:stable on this?
> >>
> >> btw, it looks like the "Clean up and error out" code in
> >> vm_module_tags_populate() could use release_pages().
>
> For the 'Clean up and error out' part:
> next_page[] array might need to be reset to NULL if user is able to
> reenable the memory allocation profiling when the above happens as the
> current page bulk alloc API are only populating NULL elements.

We shouldn't be able to re-enable memory allocation profiling once
vm_module_tags_populate() fails. In that case shutdown_mem_profiling()
call disables memory allocation profiling and sets
mem_profiling_support=false. I might have to modify
memory_allocation_profiling_sysctls to prevent users from trying to
re-enable profiling via sysfs if mem_profiling_support is set to
false. Will take a closer look at that but regarding your comment,
re-enabling profiling once it's shut down is not a valid usecase.

>
> >
> > True. I'll add that into my TODO list. Thanks!
> >
> >>
> >