Re: [PATCH v10 15/41] KVM: guest_memfd: Handle lru_add fbatch refcounts during conversion safety check

Binbin Wu [off-list ref] writes:

[...snip...]

quoted

+static bool __folio_safe_for_conversion(struct folio *folio,
+					enum lru_cache_drained *drained)
+{
+	const int filemap_get_folios_refcount = 1;
+

Nit:
After adding the helper, the use of filemap_get_folios_refcount seems
less obvious. It introduces unnecessary tight coupling with the caller,
though it has only one caller currently.

Is it better to pass the value as extra_refs, similar to what
lru_cache_drain_for_folio() does?

David also suggested [1] something similar, please see
https://lore.kernel.org/all/4c638fc5-5a74-43d0-b5bf-d7ef893cb994@kernel.org/ (local),

Please add on to that thread if you disagree with the suggestions!

quoted

+	if (folio_maybe_dma_pinned(folio) || folio_mapped(folio))
+		return false;
+
+	lru_cache_drain_for_folio(folio, filemap_get_folios_refcount,
+				  drained);
+
+	return folio_ref_count(folio) ==
+	       folio_nr_pages(folio) + filemap_get_folios_refcount;
+}
+

[...snip...]