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Message-ID: <20231002145127.0000685e@Huawei.com>
Date: Mon, 2 Oct 2023 14:51:27 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Gregory Price <gourry.memverge@...il.com>
CC: <linux-mm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
<linux-arch@...r.kernel.org>, <linux-api@...r.kernel.org>,
<linux-cxl@...r.kernel.org>, <luto@...nel.org>,
<tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
<dave.hansen@...ux.intel.com>, <hpa@...or.com>, <arnd@...db.de>,
<akpm@...ux-foundation.org>, <x86@...nel.org>,
Gregory Price <gregory.price@...verge.com>
Subject: Re: [RFC v2 3/5] mm/migrate: refactor add_page_for_migration for
code re-use
On Tue, 19 Sep 2023 19:09:06 -0400
Gregory Price <gourry.memverge@...il.com> wrote:
> add_page_for_migration presently does two actions:
> 1) validates the page is present and migratable
> 2) isolates the page from LRU and puts it into the migration list
>
> Break add_page_for_migration into 2 functions:
> add_page_for_migration - isolate the page from LUR and add to list
> add_virt_page_for_migration - validate the page and call the above
>
> add_page_for_migration does not require the mm_struct and so can be
> re-used for a physical addressing version of move_pages
>
> Signed-off-by: Gregory Price <gregory.price@...verge.com>
A few things inline.
> ---
> mm/migrate.c | 83 +++++++++++++++++++++++++++++++---------------------
> 1 file changed, 50 insertions(+), 33 deletions(-)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index dbe436163d65..1123d841a7f1 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -2042,52 +2042,33 @@ static int do_move_pages_to_node(struct list_head *pagelist, int node)
> }
>
> /*
> - * Resolves the given address to a struct page, isolates it from the LRU and
> - * puts it to the given pagelist.
> + * Isolates the page from the LRU and puts it into the given pagelist
> * Returns:
> * errno - if the page cannot be found/isolated
Is found still meaningful for what is in here?
> * 0 - when it doesn't have to be migrated because it is already on the
> * target node
> * 1 - when it has been queued
> */
> -static int add_page_for_migration(struct mm_struct *mm, const void __user *p,
> - int node, struct list_head *pagelist, bool migrate_all)
> +static int add_page_for_migration(struct page *page, int node,
> + struct list_head *pagelist, bool migrate_all)
> {
> - struct vm_area_struct *vma;
> - unsigned long addr;
> - struct page *page;
> int err;
> bool isolated;
>
> - mmap_read_lock(mm);
> - addr = (unsigned long)untagged_addr_remote(mm, p);
> -
> - err = -EFAULT;
> - vma = vma_lookup(mm, addr);
> - if (!vma || !vma_migratable(vma))
> - goto out;
> -
> - /* FOLL_DUMP to ignore special (like zero) pages */
> - page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP);
> -
> - err = PTR_ERR(page);
> - if (IS_ERR(page))
> - goto out;
> -
> err = -ENOENT;
> if (!page)
> goto out;
As noted below - this check is now duplicated. Might make sense
of course, but not obvious if it was intended.
>
> if (is_zone_device_page(page))
> - goto out_putpage;
> + goto out;
>
> err = 0;
> if (page_to_nid(page) == node)
> - goto out_putpage;
> + goto out;
>
> err = -EACCES;
> if (page_mapcount(page) > 1 && !migrate_all)
> - goto out_putpage;
> + goto out;
>
> if (PageHuge(page)) {
> if (PageHead(page)) {
> @@ -2101,7 +2082,7 @@ static int add_page_for_migration(struct mm_struct *mm, const void __user *p,
> isolated = isolate_lru_page(head);
> if (!isolated) {
> err = -EBUSY;
> - goto out_putpage;
> + goto out;
> }
>
> err = 1;
> @@ -2110,12 +2091,48 @@ static int add_page_for_migration(struct mm_struct *mm, const void __user *p,
> NR_ISOLATED_ANON + page_is_file_lru(head),
> thp_nr_pages(head));
> }
> -out_putpage:
> - /*
> - * Either remove the duplicate refcount from
> - * isolate_lru_page() or drop the page ref if it was
> - * not isolated.
> - */
> +out:
Given nothing to do here now, perhaps remove to early returns
as that may simplify some error paths.
> + return err;
> +}
> +
> +/*
> + * Resolves the given address to a struct page, isolates it from the LRU and
> + * puts it to the given pagelist.
> + * Returns:
> + * errno - if the page cannot be found/isolated
> + * 0 - when it doesn't have to be migrated because it is already on the
> + * target node
> + * 1 - when it has been queued
> + */
> +static int add_virt_page_for_migration(struct mm_struct *mm,
> + const void __user *p, int node, struct list_head *pagelist,
> + bool migrate_all)
> +{
> + struct vm_area_struct *vma;
> + unsigned long addr;
> + struct page *page;
> + int err = -EFAULT;
> +
> + mmap_read_lock(mm);
> + addr = (unsigned long)untagged_addr_remote(mm, p);
> +
> + vma = vma_lookup(mm, addr);
> + if (!vma || !vma_migratable(vma))
> + goto out;
> +
> + /* FOLL_DUMP to ignore special (like zero) pages */
> + page = follow_page(vma, addr, FOLL_GET | FOLL_DUMP);
> +
> + err = PTR_ERR(page);
> + if (IS_ERR(page))
> + goto out;
> +
> + err = -ENOENT;
> + if (!page)
> + goto out;
You do this here then again in add_page_for_migration(). Does it
need to be in both places?
> +
> + err = add_page_for_migration(page, node, pagelist, migrate_all);
> +
> put_page(page);
> out:
> mmap_read_unlock(mm);
> @@ -2211,7 +2228,7 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
> * Errors in the page lookup or isolation are not fatal and we simply
> * report them via status
> */
> - err = add_page_for_migration(mm, p, current_node, &pagelist,
> + err = add_virt_page_for_migration(mm, p, current_node, &pagelist,
> flags & MPOL_MF_MOVE_ALL);
>
> if (err > 0) {
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