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SubjectRe: [PATCH 05/18] MM: reclaim mustn't enter FS for SWP_FS_OPS swap-space
On Fri, Dec 17, 2021 at 10:48:22AM +1100, NeilBrown wrote:
> +static bool test_may_enter_fs(struct page *page, gfp_t gfp_mask)
> +{
> + if (gfp_mask & __GFP_FS)
> + return true;
> + if (!PageSwapCache(page) || !(gfp_mask & __GFP_IO))
> + return false;
> + /* We can "enter_fs" for swap-cache with only __GFP_IO
> + * providing this isn't SWP_FS_OPS.
> + * ->flags can be updated non-atomicially (scan_swap_map_slots),
> + * but that will never affect SWP_FS_OPS, so the data_race
> + * is safe.
> + */
> + return !data_race(page_swap_info(page)->flags & SWP_FS_OPS);

Nit: the normal kernel comment style uses an empty

/*

line to start the comment.

> @@ -1514,8 +1529,7 @@ static unsigned int shrink_page_list(struct list_head *page_list,
> if (!sc->may_unmap && page_mapped(page))
> goto keep_locked;
>
> - may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
> - (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
> + may_enter_fs = test_may_enter_fs(page, sc->gfp_mask);
>
> /*
> * The number of dirty pages determines if a node is marked
> @@ -1683,7 +1697,8 @@ static unsigned int shrink_page_list(struct list_head *page_list,
> goto activate_locked_split;
> }
>
> - may_enter_fs = true;
> + may_enter_fs = test_may_enter_fs(page,
> + sc->gfp_mask);

Now that may_enter_fs is always reset using test_may_enter_fs, do we
even need the local variable?

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