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Tashkinov" Subject: mm: tmpfs: huge=always Kconfig help understates severe space amplification (follow up) To: d@ilvokhin.com Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, david@kernel.org Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable X-Provags-ID: V03:K1:EakrhKYLSKK9kx8IDSMb5I5bcILvuCw+uClaAE/S+xoPYkvJyra VEhcKPmSYzRezCLX432l53KamuLLNtrFo+JFWWNTX7r0exCRGd8f88OU7GVQCEl3WLJY0Wg juL9fPcWP6DzUZW0AoRemP81gboGcr1uesUG5EGfWLoWEp7XpvGDl8uDSbFwqN1PgKYNQZI VSjNmqACtoneWoSXYkYVg== X-Spam-Flag: NO UI-OutboundReport: notjunk:1;M01:P0:PZT2iqREkeo=;KfkeL8/uE70dCQPrNUltOA5sr06 MVDWZFWi13xHm6aMUpm2qt1Z33Xeba/Rb+bb9IdC8JthyA7FJ4a0AeHunq50GG8pphu+CKqDB /h3G+WQva2eUA7hN4dN0YkyTrmsrfCxcXxjVJlWrw1zO8UKu6UVaVnztKaEzWSA9a4l46+Mm0 S4paNELYJEZPpBc8cmw084rlBWy95gI7zISOq8eRiodl/vbCTDq/51WVWDYfUMJLWwpfMzIeU TLqhrxRA1827kcNBNkypTl0Frd8EVkOAy//WTAr4h2TtCdPDqKcbNTk5Bttus7PC0gV+8HnQ0 IIf1cZ7tWThsFIt2md1ywFaiK9FlGdqXzGJGWiWPVh0HJK8rYCGkkBaQaHH6DubEqFnY/cw8S 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Although this is technically correct allocation accounting, it makes=20 identifying the cause quite difficult. Both df and du show an almost=20 full filesystem, while neither explains that huge-page allocation=20 overhead is responsible for most of the consumption. Only comparing du against du --apparent-size exposed the scale of the=20 discrepancy. This reinforces the need for explicit Kconfig documentation: users=20 investigating unexpectedly exhausted tmpfs filesystems may reasonably=20 conclude that they have accumulated excessive data, rather than=20 recognising that the selected allocation policy is consuming vastly more= =20 space than the contents require. I am not suggesting that GNU du is itself defective. Rather, this is a=20 diagnostic trap worth documenting alongside the configuration option. Regards, Artem