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In modern smartphones, system performances are tightly related to a variety of underlying subsystems. In particular, internal storage, along the years, has become crucial because it is extensively used to access content relevant to the system and, finally, to the end user. To understand its role in a commercial Android smartphone and to evaluate its effects on the User experience, within the context of a real usage, we analyzed Linux page fault handling, a critical mechanism that puts pressure on storage devices and may cause system inefficiencies. A kernel tracing technique has been conceived for real-time measurement of Android applications and services on commercial smartphones. The experimental results presented in this work are derived from the use of this kernel tracing on a 64-bit Android smartphone, equipped with a ufs storage subsystem. The main subject of the study is major page fault handling, a kernel mechanism behind many end-user actions recognized at industry level as source of possible performance deterioration in a smartphone. The analysis shows that major page fault handling is dominated by read accesses to ufs (between 30% and 40% of the total time), and that the related storage traffic is significantly affected by the ReadAhead mechanism, which is not always efficient.