What kind of eviction policy the disk Cache follows and it does not work when it is less than 5 MB

If I set the capacity of the disk cache to less than 5MB, It doesn't work.

Through the print statement, I checked that the value of the currentDiskUsage did not rise at all, and I also checked that the image has been making network requests every time because there is no cached data even if I shut down and run the app again. I'm simply wondering why this is happening.

Also, I wonder what kind of eviction policy the disk cache follows. I was so curious that I tried to find out through the link [here], but there seems to be no implementation of disk cache at all.

Below is the code I used. I'm attaching it together just in case.

import UIKit

protocol Cacheable {
    func getCachedResponse(
        for path: String,
        completion: @escaping (Result<Data, CacheError>) -> Void
    )
    func save(
        for path: String,
        data: Data
    )
}

final class CacheManager {
    
    static let shared = CacheManager()
    
    private let imageCache: URLCache
    
    init() {
        imageCache = URLCache(
            memoryCapacity: 4 * 1024 * 1024, // 4MB
            diskCapacity: 4 * 1024 * 1024 // 4MB
        )
    }
}

extension CacheManager: Cacheable {
    
    func getCachedResponse(
        for path: String,
        completion: @escaping (Result<Data, CacheError>) -> Void
    ) {
        if let url = URL(string: path),
           let cachedResponse = imageCache.cachedResponse(for: URLRequest(url: url)) {
            completion(.success(cachedResponse.data))
            return
        }
        completion(.failure(.noCachedResponse))
    }
    
    func save(
        for path: String,
        data: Data
    ) {
        guard let url = URL(string: path) else { return }
        let response = URLResponse(
            url: url,
            mimeType: nil,
            expectedContentLength: 0,
            textEncodingName: nil
        )
        if let uiImage = UIImage(data: data),
           let compressedData = uiImage.jpegData(compressionQuality: 0.8) {
            #if DEBUG
            let formmatter = ByteCountFormatter()
            formmatter.allowedUnits = [.useMB]
            formmatter.countStyle = .file
            print("""
            === Original size: \(formmatter.string(fromByteCount: Int64(data.count)))
            === Cached size: \(formmatter.string(fromByteCount: Int64(compressedData.count)))
            """)
            #endif
            let cachedResponse = CachedURLResponse(
                response: response,
                data: compressedData
            )
            imageCache.storeCachedResponse(
                cachedResponse,
                for: URLRequest(url: url)
            )
        }
    }
}